https://codeforces.com/contest/1131/problem/B

题解：

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,q;
ll ans,cnt,flag,temp;
ll a,b,x,y;
char str;
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    scanf("%d",&n);
    ans=1;
    for(int i=1;i<=n;i++){
        scanf("%I64d%I64d",&a,&b);
        int low=max(x,y);
        if(x==y)low++;
        int high=min(a,b);
        ans+=(high-low+1>0?high-low+1:0);
        x=a,y=b;
    }
    cout << ans << endl;
    //scanf("%d",&t);
    //while(t--){}
    //cout << "Hello world!" << endl;
    return 0;
}