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.*;
import static java.lang.Math.*;

public class Main {
    private static boolean oj = System.getProperty("ONLINE_JUDGE") != null;
    private static Reader in;
    private static PrintWriter out;
    ////////////////////////////////////////////////////////////////////////////////////////////////////
    private static int min(int... a){int min=a[0]; for(int i:a) min=Math.min(min, i); return min;}
    private static int max(int... a){int max=a[0]; for(int i:a) max=Math.max(max, i); return max;}
    private static long min(long... a){long min=a[0]; for(long i:a)min=Math.min(min, i); return min;}
    private static long max(long... a){long max=a[0]; for(long i:a)max=Math.max(max, i); return max;}
    private static String strm(String str, long m) {
        String ans="";
        while(m>0) {
            if(m%2==1) ans=ans.concat(str);
            str=str.concat(str); m>>=1;
        } return ans;
    }
    private static long mod(long a, long mod) {long res = a%mod; return res>=0 ? res : res+mod;}
    private static int mod(int a, int mod) {int res = a%mod; return res>=0 ? res : res+mod;}
    private static long modpow(long x, int n, int mod) {
        long res = 1;
        for (long p = x; n > 0; n >>= 1, p = mod((mod(p, mod)*mod(p, mod)),  mod)) {
            if ((n & 1) != 0) res = mod(mod(res, mod) * mod(p, mod), mod);
        }
        return res;
    }
    private static long gcd(long a, long b) {return b == 0 ? Math.abs(a) : gcd(b, a % b);}
    private static int gcd(int a, int b) {return b == 0 ? Math.abs(a) : gcd(b, a % b);}
    private static long gcd(long... a) {long gcd=a[0]; for(long x:a) gcd=gcd(gcd, x); return gcd;}
    private static int gcd(int... a) {int gcd=a[0]; for(int x:a) gcd=gcd(gcd, x); return gcd;}
    private static long lcm(long a, long b) {return Math.abs(a / gcd(a, b) * b);}
    private static class Pair {
        public int x, y;
        public Pair(int x, int y) {
            this.x = x;
            this.y = y;
        }
        @Override
        public boolean equals(Object obj) {
            if (obj == this) return true;
            if (!(obj instanceof Pair)) return false;
            Pair pair = (Pair)obj;
            return this.x == pair.x && this.y == pair.y;
        }

        @Override
        public int hashCode() {
            return (this.x+" "+this.y).hashCode();
        }
    }
    private static class Triplet {
        public int x, y, z;
        public Triplet(int x, int y, int z) {
            this.x = x;
            this.y = y;
            this.z = z;
        }
        @Override
        public boolean equals(Object obj) {
            if (obj == this) return true;
            if (!(obj instanceof Triplet)) return false;
            Triplet triplet = (Triplet)obj;
            return this.x == triplet.x && this.y == triplet.y && this.z == triplet.z;
        }

        @Override
        public int hashCode() {
            return (this.x+" "+this.y+" "+this.z).hashCode();
        }
    }
    ////////////////////////////////////////////////////////////////////////////////////////////////////
    static class Reader {
        private BufferedReader br;
        private StringTokenizer token;
        protected Reader(FileReader obj) {
            br = new BufferedReader(obj, 32768);
            token = null;
        }
        protected Reader() {
            br = new BufferedReader(new InputStreamReader(System.in), 32768);
            token = null;
        }
        protected String next() {
            while(token == null || !token.hasMoreTokens()) {
                try {
                    token = new StringTokenizer(br.readLine());
                } catch (Exception e) {e.printStackTrace();}
            } return token.nextToken();
        }
        protected String nextLine() {
            String str="";
            try {
                str = br.readLine();
            } catch (Exception e) {e.printStackTrace();}
            return str;
        }
        protected int nextInt() {return Integer.parseInt(next());}
        protected long nextLong() {return Long.parseLong(next());}
        protected double nextDouble() {return Double.parseDouble(next());}
        protected long[] nextLongArr(int n) {
            long[] arr = new long[n]; for(int i=0; i<n; i++) arr[i] = nextLong(); return arr;
        }
        protected int[] nextIntArr(int n) {
            int[] arr = new int[n]; for(int i=0; i<n; i++) arr[i] = nextInt(); return arr;
        }
    }
    public static final int mod = 1_000_000_007;
    private static void solve() throws Exception {
        int n = in.nextInt();
        int ans = 1;
        int cx = 0, cy = 0;
        int[][] arr = new int[n][2];
        for (int i=0; i<n; i++) {
            arr[i][0] = in.nextInt(); arr[i][1] = in.nextInt();
            if (arr[i][0] == 0 || arr[i][1] == 0) {cx = arr[i][0]; cy = arr[i][1]; continue;}
            if (min(arr[i][0], arr[i][1]) >= max(cx, cy) && !(arr[i][0] == cx && arr[i][1] == cy)) {
                ans += min(arr[i][0], arr[i][1]) - max(cx, cy) + 1;
                if (cx == cy) ans--;
            }
            cx = arr[i][0]; cy = arr[i][1];
        }
        out.printf("%d\n", ans);
    }
    private static void run() throws Exception
    {
        // in = new Reader();
//        in = new Reader(new FileReader("input.txt"));
//        out = new PrintWriter(new FileWriter("output.txt"));
        in = oj ? new Reader() : new Reader(new FileReader("/home/raiden/Desktop/input.txt"));
        out = new PrintWriter(System.out);
        long ti = System.currentTimeMillis();
        solve(); out.flush();
        if (!oj) System.out.println("\n"+(System.currentTimeMillis()-ti)+"ms");
    }
    public static void main(String[] args) throws Exception {run();}
}