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.
import java.io.*;
import java.util.InputMismatchException;
import java.util.Random;

/**
 * @author tainic on Feb 23, 2019
 */
public class b {

    private static boolean LOCAL;
    static {
        try { LOCAL = "aurel".equalsIgnoreCase(System.getenv().get("USER")); } catch (Exception e){}
    }

    private static final String TEST =
        "3\n" +
            "2 0\n" +
            "3 1\n" +
            "3 4";

    void solve(InputReader in, PrintWriter out) {
        int n = in.nextInt();
        long a = 0;
        long b = 0;
        long ans = 1;
        while (n-- > 0) {
            if (a == b) ans--;
            long c = in.nextLong();
            long d = in.nextLong();
            ans += Math.max(0, Math.min(c, d) - Math.max(a, b) + 1);
            a = c;
            b = d;
        }
        out.println(ans);
    }

    //region util
    static class Util {

        private static final Random R = new Random();

        public static void sort(int[] a) {
            sort(a, 0, a.length - 1);
        }

        private static void sort(int[] a, int from, int to) {
            if (from >= to) {
                return;
            }

            // partition
            int pivotIndex = R.nextInt(to - from + 1) + from;
            int pivot = a[pivotIndex];
            // maintain this invariant, at each step i:
            // a[j] <  pivot, for j = fromIndex to lt - 1
            // a[j] == pivot, for j = lt to i - 1
            // a[j] >  pivot, for j = gt + 1 to toIndex
            int lt = from;
            int gt = to;
            int i = lt;
            while (i <= gt) {
                int cmp = a[i] - pivot;
                if (cmp < 0) {
                    swap(a, i, lt);
                    i++;
                    lt++;
                } else if (cmp > 0) {
                    swap(a, i, gt);
                    gt--;
                } else {
                    i++;
                }
            }

            // sort left and right
            sort(a, from, lt - 1);
            sort(a, gt + 1, to);
        }

        public static int findFirst(int[] a, int key) {
            return findFirstOrLast(a, key, 0, a.length - 1, -1);
        }

        public static int findLast(int[] a, int key) {
            return findFirstOrLast(a, key, 0, a.length - 1, 1);
        }

        public static int findFirstOrLast(int[] a, int key, int fromIndex, int toIndex, int dir) {
            int left = fromIndex;
            int right = toIndex;
            while (left <= right) {
                int mid = (left + right) >>> 1;
                int cmp = key - a[mid];
                if (cmp > 0) {
                    left = mid + 1;
                } else if (cmp < 0) {
                    right = mid - 1;
                } else if (dir == -1 && mid > fromIndex && a[mid - 1] == key) {
                    right = mid - 1;
                } else if (dir == 1 && mid < toIndex && a[mid + 1] == key) {
                    left = mid + 1;
                } else {
                    return mid;
                }
            }
            return -left - 1;
        }

        public static void swap(int[] a, int i, int j) {
            if (i != j) {
                int ai = a[i];
                a[i] = a[j];
                a[j] = ai;
            }
        }

        public static int[] readInts(InputReader in, int k) {
            int[] a = new int[k];
            for (int i = 0; i < k; i++) {
                a[i] = in.nextInt();
            }
            return a;
        }

    }
    //endregion

    //region main
    public static void main(String[] args) throws Exception {
        long t = System.currentTimeMillis();

        try (
            InputReader in = new StreamInputReader(!LOCAL ? System.in : new ByteArrayInputStream(TEST.getBytes()));
            PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out, 2048), false)
        ) {
            new b().solve(in, out);
        }

        System.err.println("time: " + (System.currentTimeMillis() - t) + "ms");
    }
    //endregion

    //region fast io
    abstract static class InputReader implements AutoCloseable {

        public abstract int read();

        public int nextInt() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public long nextLong() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public String next() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }

        public boolean isSpaceChar(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
    }

    static class StreamInputReader extends InputReader {

        private InputStream stream;
        private byte[] buf;
        private int curChar, numChars;

        public StreamInputReader(InputStream stream) {
            this(stream, 2048);
        }

        public StreamInputReader(InputStream stream, int bufSize) {
            this.stream = stream;
            this.buf = new byte[bufSize];
        }

        @Override
        public int read() {
            if (numChars == -1) {
                throw new InputMismatchException();
            }
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (numChars <= 0) {
                    return -1;
                }
            }
            return buf[curChar++];
        }

        @Override
        public void close() throws Exception {
            stream.close();
        }

    }
    //endregion

    //region imports
    //endregion

}