#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;
    vector<int> a(n), b(n);
    for (int i = 1; i < n; i++) {
        cin >> a[i] >> b[i];
        as += a[i];
        bs += b[i];
    }

    int minv = max(bs - as, 0);
    int maxv = bs;
    int ans = 0;
    for (int a1 = minv; a1 <= maxv; a1++) {
        a[0] = a1;
        int aa = as + a1;
        int bb = aa;
        b[0] = bb - bs;
        if (b[0] < 0) continue;

        bool f = true;
        for (int i = 0; i < n; i++) {
            if (a[i] <= bb - b[i] && b[i] <= aa - a[i]) continue;
            f = false;
            break;
        }
        ans += f;
    }
    cout << ans << "\n";
    return 0;
}