Codeforces 1131B（贪心）

#include <cstdio>
#include <cctype>
#include <iostream>
#include <algorithm>
#define ri readint()
#define gc getchar()
using namespace std;

int readint() {
    int x = 0, s = 1, c = gc;
    while (c <= 32) c = gc;
    if (c == '-')   s = -1, c = gc;
    for (; isdigit(c); c = gc)
        x = x * 10 + c - 48;
    return x * s;
}

int n, a, b, lasta, lastb;
long long ans;

int main() {
    for (n = ri; n; n--) {
        a = ri, b = ri;
        ans += max(0, min(a, b) - max(lasta, lastb) + 1);
        lasta = a, lastb = b;
        if (lasta == lastb) {
            lasta++;
            lastb++;
        }
    }
    cout << ans << endl;
    return 0;
}