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.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

public class d {
    static  BufferedReader s = new BufferedReader(new InputStreamReader(System.in));;
    public static void main(String[] args) throws IOException {
        StringBuilder sb = new StringBuilder();
        String[] s1 = s();

         int n=i(s1[0]);
           int a=0;int b=0;
           int ans=1;
           for(int i=0;i<n;i++){
               String[] s3=s();
               int na=i(s3[0]);int nb=i(s3[1]);
               if( Math.min(na,nb)-Math.max(a,b)>=0){
                   if(a==b){
                       ans+=Math.min(na,nb)-Math.max(a,b);
                   }else
                  ans+=Math.min(na,nb)-Math.max(a,b)+1;
               }a=na;b=nb;
           }
        System.out.println(ans);
    }

    static String[] s()throws  IOException{
        return s.readLine().trim().split("\\s+");
    }
    static int i(String ss){
        return Integer.parseInt(ss);
    }
    static long l(String ss) {return Long.parseLong(ss);}
    static String lexographicallysmallest(String s) {
        if (s.length() % 2 == 1) return s;
        String s1 =lexographicallysmallest(s.substring(0, s.length()/2));
        String s2 = lexographicallysmallest(s.substring(s.length()/2, s.length()));
        if (s1.compareTo(s2)<0) return s1 + s2;
        else return s2 + s1;
    }
    public static int countSetBits(int n) {
        return (BitsSetTable256[n & 0xff]
                + BitsSetTable256[(n >> 8) & 0xff]
                + BitsSetTable256[(n >> 16) & 0xff]
                + BitsSetTable256[n >> 24]);
    }
    static int[] BitsSetTable256 ;
    public static void initialize(int n) {
        BitsSetTable256[0] = 0;
        for (int i = 0; i <=Math.pow(2,n); i++) {
            BitsSetTable256[i] = (i & 1) + BitsSetTable256[i / 2];
        }
    }
    static  void computeLPSArray(String pat, int M, int lps[]) {
        int len = 0;
        int i = 1;
        lps[0] = 0;
        while (i < M) {
            if (pat.charAt(i) == pat.charAt(len)) {
                len++;
                lps[i] = len;
                i++;
            }
            else
            {
                if (len != 0) {
                    len = lps[len - 1];
                }
                else
                {
                    lps[i] = len;
                    i++;
                }
            }
        }
    }
    static boolean isPrime(int n) {
        if (n <= 1) return false;
        if (n <= 3) return true;

        if (n % 2 == 0 || n % 3 == 0) return false;

        for (int i = 5; i * i <= n; i = i + 6)
            if (n % i == 0 || n % (i + 2) == 0)
                return false;

        return true;
    }
    static long powerwithmod(long  x, long y, long p) {
        long  res = 1;
        x = x % p;
        while (y > 0) {
            if ((y & 1) == 1)
                res = (res * x) % p;
            y = y >> 1;
            x = (x * x) % p;
        }
        return res;
    }
    static long  powerwithoutmod(long x, int y) {
        long  temp;
        if( y == 0)
            return 1;
        temp = powerwithoutmod(x, y/2);
        if (y%2 == 0)
            return temp*temp;
        else
        {
            if(y > 0)
                return x * temp * temp;
            else
                return (temp * temp) / x;
        }
    }
    static void fracion(double x) {
        String a = "" + x;
        String spilts[] = a.split("\\."); // split using decimal
        int b = spilts[1].length(); // find the decimal length
        int denominator = (int) Math.pow(10, b); // calculate the denominator
        int numerator = (int) (x * denominator); // calculate the nerumrator Ex
        // 1.2*10 = 12
        int gcd = (int) gcd((long) numerator, denominator); // Find the greatest common
        // divisor bw them
        String fraction = "" + numerator / gcd + "/" + denominator / gcd;
        // System.out.println((denominator/gcd));
        long x1 = modInverse(denominator / gcd, 998244353);
        //  System.out.println(x1);
        System.out.println((((numerator / gcd) % 998244353 * (x1 % 998244353)) % 998244353));
    }
    static int bfs(int i1, ArrayList<Integer>[] h, int[] vis, int n,int val1) {
        Queue<Integer> q = new LinkedList<Integer>();
        q.add(i1);Queue<Integer> aq=new LinkedList<Integer>();
        aq.add(0);
        while(!q.isEmpty()){
            int i=q.poll();
            int val=aq.poll();
            if(i==n){
                return val;
            }
            if(h[i]!=null){
                for(Integer j:h[i]){
                    if(vis[j]==0){
                        q.add(j);vis[j]=1;
                        aq.add(val+1);}
                }
            }
        }return -1;
    }
    static long gcd(long a, long b) {
        if (b == 0)
            return a;
        return gcd(b, a % b);
    }
    static long modInverse(long a, long m)
    {
        return (powerwithmod(a, m - 2, m));
    }
    static int MAXN;
    static int[] spf;
    static void sieve() {
        spf[1] = 1;
        for (int i=2; i<MAXN; i++)
            spf[i] = i;
        for (int i=4; i<MAXN; i+=2)
            spf[i] = 2;
        for (int i=3; i*i<MAXN; i++)
        {
            if (spf[i] == i)
            {
                for (int j=i*i; j<MAXN; j+=i)

                    if (spf[j]==j)
                        spf[j] = i;
            }
        }
    }
    static ArrayList<Integer> getFactorizationUsingSeive(int x) {
        ArrayList<Integer> ret = new ArrayList<Integer>();
        while (x != 1)
        {
            ret.add(spf[x]);
            if(spf[x]!=0)   x = x / spf[x];
            else break;       }
        return ret;
    }
    static long[] fac ;
    static void calculatefac(long mod){
        fac[0]=1;
        for (int i = 1 ;i <= MAXN; i++)
            fac[i] = fac[i-1] * i % mod;
    }
    static long nCrModPFermat(int n, int r, long mod) {
        if (r == 0)
            return 1;
        fac[0] = 1;
        return (fac[n]*
                modInverse(fac[r], mod)
                % mod * modInverse(fac[n-r], mod)
                % mod) % mod;
    } }
    class Student {
    int  l;long r;
    public Student(int l, long r) {
        this.l = l;
        this.r = r;
    }

    public String toString()
    {
        return this.l+" ";
    }
}
    class Sortbyroll implements Comparator<Student> {

    public int compare(Student a, Student b){
        if(a.r<b.r) return -1;
        else if(a.r==b.r){
            if(a.r==b.r){
                return 0;
            }
            if(a.r<b.r) return -1;
            return 1;}
        return 1;  }
}
