#include <bits/stdc++.h>
using namespace std;

using ll = long long;

int main() {
    int n;
    cin >> n;
    vector<int> a(n - 1), b(n - 1);
    int sum_a = 0, sum_b = 0;
    for (int i = 0; i < n - 1; i++) {
        cin >> a.at(i) >> b.at(i);
        sum_a += a.at(i);
        sum_b += b.at(i);
    }

    int cnt = 0;
    int d = sum_a - sum_b;
    for (int a0 = 0; a0 <= sum_b; a0++) {
        int b0 = a0 + d;
        if (b0 < 0) continue;

        bool ok = true;
        for (int i = 0; i < n - 1; i++) {
            if (sum_b - b.at(i) + b0 < a.at(i)) ok = false;
        }
        if (ok) cnt++;
    }
    cout << cnt << endl;
}