#include <bits/stdc++.h>

using namespace std;

using ll = long long;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    int as = 0, bs = 0;
    for (int i = 1; i < n; i++) {
        int a, b;
        cin >> a >> b;
        as += a;
        bs += b;
    }

    cout << bs - max(bs - as, 0) + 1 << endl;
    return 0;
}