You still have partial information about the score during the historic football match. You are given a set of pairs (a_i, b_i), indicating that at some point during the match the score was "a_i: b_i". It is known that if the current score is «x:y», then after the goal it will change to "x+1:y" or "x:y+1". What is the largest number of times a draw could appear on the scoreboard?

The pairs "a_i:b_i" are given in chronological order (time increases), but you are given score only for some moments of time. The last pair corresponds to the end of the match.

Input

The first line contains a single integer n (1 ≤ n ≤ 10000) — the number of known moments in the match.

Each of the next n lines contains integers a_i and b_i (0 ≤ a_i, b_i ≤ 10^9), denoting the score of the match at that moment (that is, the number of goals by the first team and the number of goals by the second team).

All moments are given in chronological order, that is, sequences x_i and y_j are non-decreasing. The last score denotes the final result of the match.

Output

Print the maximum number of moments of time, during which the score was a draw. The starting moment of the match (with a score 0:0) is also counted.

Examples

Input

3
2 0
3 1
3 4


Output

2


Input

3
0 0
0 0
0 0


Output

1


Input

1
5 4


Output

5

Note

In the example one of the possible score sequences leading to the maximum number of draws is as follows: 0:0, 1:0, 2:0, 2:1, 3:1, 3:2, 3:3, 3:4.
//package com.company;

import java.util.*;
import java.io.*;
import java.lang.*;

public class Main {

    public static Input input;
    public static Output output;

    public static void main(String[] args) throws Exception {
        input = new Input();
        output = new Output();
        int quantity = input.ReadInt();
        int first = 0;
        int second = 0;
        int answer = 1;
        for (int i = 0;i<quantity; i++){
            int[] base = input.ReadArrayInt(" ");
            if (base[0] != first || base[1] != second) {
                int min = Math.max(first, second);
                int max = Math.min(base[0], base[1]);
                if (max >= min) {
                    answer += max - min + ((min > Math.min(first, second)) ? 1 : 0);
                }
                first = base[0];
                second = base[1];
            }
        }
        System.out.println(answer == 0 ? 1 : answer);
    }

}

class method {

    public static int gcd(int a, int b) { // NOD
        if (b == 0) {
            return a;
        }
        return gcd(b, a % b);
    }

    public static long gcd(long a, long b) {
        if (b == 0) {
            return a;
        }
        return gcd(b, a % b);
    }

    public static int lcm(int a, int b) { // NOK
        return a / gcd(a, b) * b;
    }

    public static long lcm(long a, long b) {
        return a / gcd(a, b) * b;
    }

    public static void exit() throws Exception {
        Main.output.write.flush();
        Main.input.read.close();
        Main.output.write.close();
    }
}

class graph {

    private static int[][] base;
    private static boolean[] used;
    public static int quantity = 0;
    private static Integer[] pred;

    public static void start(int length) {
        used = new boolean[length];
        pred = new Integer[length];
    }

    public static void RibMatrixToDefault(int length) throws Exception {
        start(length);
        base = new int[length][];
        int FirstSize;
        int SecondSize;
        int[] rib;
        int[] FirstArray;
        int[] SecondArray;
        int[] NewFirstArray;
        int[] NewSecondArray;
        for (int i = 0; i < length; i++) {
            rib = Arrays.stream(Main.input.ReadArrayInt(" ")).map(element -> element - 1).toArray();
            FirstArray = base[rib[0]];
            SecondArray = base[rib[1]];
            if (FirstArray == null) {
                FirstSize = 0;
            } else {
                FirstSize = FirstArray.length;
            }
            if (SecondArray == null) {
                SecondSize = 0;
            } else {
                SecondSize = SecondArray.length;
            }
            NewFirstArray = new int[FirstSize + 2];
            NewSecondArray = new int[SecondSize + 2];
            for (int index = 0; index < Math.max(FirstSize, SecondSize); index++) {
                if (index < FirstSize) {
                    NewFirstArray[index] = FirstArray[index];
                }
                if (index < SecondSize) {
                    NewSecondArray[index] = SecondArray[index];
                }
            }
            NewFirstArray[FirstSize] = rib[1];
            NewSecondArray[SecondSize] = rib[0];
            NewFirstArray[FirstSize + 1] = 1;
            NewSecondArray[SecondSize + 1] = 1;
            base[rib[0]] = NewFirstArray;
            base[rib[1]] = NewSecondArray;
        }
    }

    public static void AdjacencyMatrixToDefault(int length, int dont) throws Exception {
        start(length);
        base = new int[length][];
        List<Integer> buffer = new ArrayList<>();
        int[] InputArray;
        int size;
        for (int i = 0; i < length; i++) {
            InputArray = Main.input.ReadArrayInt(" ");
            for (int index = 0; index < length; index++) {
                if (i != index && InputArray[index] != dont) {
                    buffer.add(index);
                    buffer.add(InputArray[index]);
                }
            }
            base[i] = buffer.stream().mapToInt(element -> element).toArray();
            buffer.clear();
        }
    }

    public static void dfs(int position) throws Exception {
        used[position] = true;
        quantity++;
        int next;
        for (int index = 0; index < base[position].length; index += 2) {
            next = base[position][index];
            if (!used[next]) {
                pred[next] = position;
                dfs(next);
            } else {
                if (next != pred[position]) { // if cycle
                    throw new Exception();
                }
            }
        }
    }

    public static int dijkstra(int start, int stop, int size) {
        start--;
        stop--;
        int[] dist = new int[size];
        for (int i = 0; i < size; i++) {
            if (i != start) {
                dist[i] = Integer.MAX_VALUE;
            }
            pred[i] = start;
        }
        Queue<int[]> queue = new PriorityQueue<>((int[] first, int[] second) -> Integer.compare(first[1], second[1]));
        queue.add(new int[]{start, 0});
        int position;
        int[] GetQueue;
        while (queue.size() != 0) {
            GetQueue = queue.poll();
            position = GetQueue[0];
            if (GetQueue[1] > dist[position]) {
                continue;
            }
            for (int index = 0; index < base[position].length; index += 2) {
                if (dist[position] + base[position][index + 1] < dist[base[position][index]] && !used[base[position][index]]) {
                    dist[base[position][index]] = dist[position] + base[position][index + 1];
                    pred[base[position][index]] = position;
                    queue.add(new int[]{base[position][index], dist[base[position][index]]});
                }
            }
            used[position] = true;
        }
        return dist[stop] == Integer.MAX_VALUE ? -1 : dist[stop];
    }

    public static boolean FloydWarshall(int[][] base, int length, int dont) {
        for (int k = 0; k < length; k++) {
            for (int i = 0; i < length; i++) {
                for (int j = 0; j < length; j++) {
                    if (base[i][k] == dont || base[k][j] == dont) {
                        continue;
                    }
                    int total = base[i][k] + base[k][j];
                    if (base[i][j] != dont) {
                        base[i][j] = Math.min(base[i][j], total);
                    } else {
                        base[i][j] = total;
                    }
                }
            }
        }
        for (int index = 0; index < length; index++) {
            if (base[index][index] != 0) { // if cycle
                return false;
            }

        }
        return true;
    }
}

class FastSort {

    public static void SortWithoutReturn(int[] array, int ShellHeapMergeMyInsertionSort, int length) {
        sort(array, ShellHeapMergeMyInsertionSort, length);
    }

    public static int[] SortWithReturn(int[] array, int ShellHeapMergeMyInsertionSort, int length) {
        sort(array, ShellHeapMergeMyInsertionSort, length);
        return array;
    }

    private static void sort(int[] array, int ShellHeapMergeMyInsertionSort, int length) {
        Random random = new Random();
        if (ShellHeapMergeMyInsertionSort < 0 || ShellHeapMergeMyInsertionSort > 4) {
            ShellHeapMergeMyInsertionSort = random.nextInt(4);
        }
        if (ShellHeapMergeMyInsertionSort == 0) {
            ShellSort(array);
        } else if (ShellHeapMergeMyInsertionSort == 1) {
            HeapSort(array);
        } else if (ShellHeapMergeMyInsertionSort == 2) {
            MergeSort(array, 0, length - 1);
        } else if (ShellHeapMergeMyInsertionSort == 3) {
            StraightMergeSort(array, length);
        } else if (ShellHeapMergeMyInsertionSort == 4) {
            insertionSort(array);
        }
    }

    private static void StraightMergeSort(int[] array, int size) {
        if (size == 0) {
            return;
        }
        int length = (size / 2) + ((size % 2) == 0 ? 0 : 1);
        Integer[][] ZeroBuffer = new Integer[length + length % 2][2];
        Integer[][] FirstBuffer = new Integer[0][0];
        for (int index = 0; index < length; index++) {
            int ArrayIndex = index * 2;
            int NextArrayIndex = index * 2 + 1;
            if (NextArrayIndex < size) {
                if (array[ArrayIndex] > array[NextArrayIndex]) {
                    ZeroBuffer[index][0] = array[NextArrayIndex];
                    ZeroBuffer[index][1] = array[ArrayIndex];
                } else {
                    ZeroBuffer[index][0] = array[ArrayIndex];
                    ZeroBuffer[index][1] = array[NextArrayIndex];
                }
            } else {
                ZeroBuffer[index][0] = array[ArrayIndex];
            }
        }
        boolean position = false;
        int pointer0;
        int pointer;
        int pointer1;
        int number = 4;
        int NewPointer;
        int count;
        Integer[][] NewBuffer;
        Integer[][] OldBuffer;
        length = (size / 4) + ((size % 4) == 0 ? 0 : 1);
        while (true) {
            pointer0 = 0;
            count = (number / 2) - 1;
            if (!position) {
                FirstBuffer = new Integer[length + length % 2][number];
                NewBuffer = FirstBuffer;
                OldBuffer = ZeroBuffer;
            } else {
                ZeroBuffer = new Integer[length + length % 2][number];
                NewBuffer = ZeroBuffer;
                OldBuffer = FirstBuffer;
            }
            for (int i = 0; i < length; i++) {
                pointer = 0;
                pointer1 = 0;
                NewPointer = pointer0 + 1;
                if (length == 1) {
                    for (int g = 0; g < size; g++) {
                        if (pointer > count || OldBuffer[pointer0][pointer] == null) {
                            array[g] = OldBuffer[NewPointer][pointer1];
                            pointer1++;
                        } else if (pointer1 > count || OldBuffer[NewPointer][pointer1] == null) {
                            if (OldBuffer[pointer0][pointer] == null) {
                                continue;
                            }
                            array[g] = OldBuffer[pointer0][pointer];
                            pointer++;
                        } else if (OldBuffer[pointer0][pointer] >= OldBuffer[NewPointer][pointer1]) {
                            array[g] = OldBuffer[NewPointer][pointer1];
                            pointer1++;
                        } else {
                            array[g] = OldBuffer[pointer0][pointer];
                            pointer++;
                        }
                    }
                    return;
                }
                for (int g = 0; g < number; g++) {
                    if (pointer > count || OldBuffer[pointer0][pointer] == null) {
                        if (OldBuffer[NewPointer][pointer1] == null) {
                            continue;
                        }
                        NewBuffer[i][g] = OldBuffer[NewPointer][pointer1];
                        pointer1++;
                    } else if (pointer1 > count || OldBuffer[NewPointer][pointer1] == null) {
                        if (OldBuffer[pointer0][pointer] == null) {
                            continue;
                        }
                        NewBuffer[i][g] = OldBuffer[pointer0][pointer];
                        pointer++;
                    } else if (OldBuffer[pointer0][pointer] >= OldBuffer[NewPointer][pointer1]) {
                        NewBuffer[i][g] = OldBuffer[NewPointer][pointer1];
                        pointer1++;
                    } else {
                        NewBuffer[i][g] = OldBuffer[pointer0][pointer];
                        pointer++;
                    }
                }
                pointer0 += 2;
            }
            position = !position;
            length = length / 2 + (length % 2 == 0 ? 0 : 1);
            number *= 2;

        }
    }

    public static void ShellSort(int[] array) {
        int j;
        for (int gap = array.length / 2; gap > 0; gap /= 2) {
            for (int i = gap; i < array.length; i++) {
                int temp = array[i];
                for (j = i; j >= gap && array[j - gap] > temp; j -= gap) {
                    array[j] = array[j - gap];
                }
                array[j] = temp;
            }
        }
    }

    private static void HeapSort(int[] array) {
        for (int i = array.length / 2 - 1; i >= 0; i--)
            shiftDown(array, i, array.length);
        for (int i = array.length - 1; i > 0; i--) {
            swap(array, 0, i);
            shiftDown(array, 0, i);
        }
    }

    private static void shiftDown(int[] array, int i, int n) {
        int child;
        int tmp;
        for (tmp = array[i]; leftChild(i) < n; i = child) {
            child = leftChild(i);
            if (child != n - 1 && (array[child] < array[child + 1]))
                child++;
            if (tmp < array[child])
                array[i] = array[child];
            else
                break;
        }
        array[i] = tmp;
    }

    private static int leftChild(int i) {
        return 2 * i + 1;
    }

    private static void swap(int[] array, int i, int j) {
        int temp = array[i];
        array[i] = array[j];
        array[j] = temp;
    }

    private static void MergeSort(int[] array, int low, int high) {
        if (low < high) {
            int mid = (low + high) / 2;
            MergeSort(array, low, mid);
            MergeSort(array, mid + 1, high);
            merge(array, low, mid, high);
        }
    }

    private static void merge(int[] array, int low, int mid, int high) {
        int n = high - low + 1;
        int[] Temp = new int[n];
        int i = low, j = mid + 1;
        int k = 0;
        while (i <= mid || j <= high) {
            if (i > mid)
                Temp[k++] = array[j++];
            else if (j > high)
                Temp[k++] = array[i++];
            else if (array[i] < array[j])
                Temp[k++] = array[i++];
            else
                Temp[k++] = array[j++];
        }
        for (j = 0; j < n; j++)
            array[low + j] = Temp[j];
    }

    private static void insertionSort(int[] elements) {
        for (int i = 1; i < elements.length; i++) {
            int key = elements[i];
            int j = i - 1;
            while (j >= 0 && key < elements[j]) {
                elements[j + 1] = elements[j];
                j--;
            }
            elements[j + 1] = key;
        }
    }
}

class Input {

    public BufferedReader read;
    public static boolean FileInput = false;

    Input() {
        try {
            read = new BufferedReader(FileInput ? new FileReader("input.txt") : new InputStreamReader(System.in));
        } catch (Exception error) {
        }
    }

    public int ReadInt() throws Exception {
        return Integer.parseInt(read.readLine());
    }

    public long ReadLong() throws Exception {
        return Long.parseLong(read.readLine());
    }

    public String ReadString() throws Exception {
        return read.readLine();
    }

    public int[] ReadArrayInt(String split) throws Exception {
        return Arrays.stream(read.readLine().split(split)).mapToInt(Integer::parseInt).toArray();
    }

    public long[] ReadArrayLong(String split) throws Exception {
        return Arrays.stream(read.readLine().split(split)).mapToLong(Long::parseLong).toArray();
    }

    public String[] ReadArrayString(String split) throws Exception {
        return read.readLine().split(split);
    }
}

class Output {

    public BufferedWriter write;
    public static boolean FileOutput = false;

    Output() {
        try {
            write = new BufferedWriter(FileOutput ? new FileWriter("output.txt") : new OutputStreamWriter(System.out));
        } catch (Exception error) {
        }
    }

    public void WriteArray(int[] array, String split) {
        try {
            int length = array.length;
            for (int index = 0; index < length; index++) {
                write.write(Integer.toString(array[index]));
                if (index + 1 != length) {
                    write.write(split);
                }
            }
        } catch (Exception error) {
        }


    }

    public void WriteArray(long[] array, String split) {
        try {
            int length = array.length;
            for (int index = 0; index < length; index++) {
                write.write(Long.toString(array[index]));
                if (index + 1 != length) {
                    write.write(split);
                }
            }
        } catch (Exception error) {
        }
    }

    public void WriteArray(String[] array, String split) {
        try {
            int length = array.length;
            for (int index = 0; index < length; index++) {
                write.write(array[index]);
                if (index + 1 != length) {
                    write.write(split);
                }
            }
        } catch (Exception error) {
        }
    }

    public void WriteArray(boolean[] array, String split) {
        try {
            int length = array.length;
            for (int index = 0; index < length; index++) {
                write.write(Boolean.toString(array[index]));
                if (index + 1 != length) {
                    write.write(split);
                }
            }
        } catch (Exception error) {
        }
    }

    public void WriteInt(int number, String split) {
        try {
            write.write(Integer.toString(number));
            write.write(split);
        } catch (Exception error) {
        }
    }

    public void WriteString(String word, String split) {
        try {
            write.write(word);
            write.write(split);
        } catch (Exception error) {
        }
    }

    public void WriteLong(Long number, String split) {
        try {
            write.write(Long.toString(number));
            write.write(split);
        } catch (Exception error) {
        }
    }
}