#include <bits/stdc++.h>
using namespace std;
#define int long long
int n, a, b, cnt = 0;
int ship[199999999];
signed main()
{
    scanf("%lld", &n);
    for(int i = 1; i <= n; i++){
        scanf("%lld %lld", &a, &b);
        for(int i = a; i <= b; i++){
            ship[i] = 1;
        }
    }
    for(int i = 1; i <= n; i++){
        cnt += ship[i];
    }
    printf("%lld", cnt);
    return 0;
}