#include <bits/stdc++.h>
using namespace std;
int main() {
    int n; cin >> n;
    int asum = 0; int bsum = 0;
    int maxi = 0;
    for (int i = 0; i < n-1; i++) {
        int c, d; cin >> c >> d;
        asum += c; bsum += d;
        maxi = max(maxi, c+d);
    }
    int ans = 0;
    for (int a = 0; a <= bsum; a++) {
        if (asum+a >= maxi) ans++;
    }
    cout << ans << endl;
    return 0;
}