#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    // Ai <= sum(B) - Bi
    // A1 + sum(A) == B1 + sum(B)
    int N; cin >> N; N--;
    vector<int> A(N), B(N);
    rep(i,N) cin >> A[i] >> B[i];
    int sumA = accumulate(A.begin(), A.end(), 0);
    int sumB = accumulate(B.begin(), B.end(), 0);
    int ans = 0;
    for(int A1 = 0; A1 <= sumB; A1++) {
        int B1 = A1 + sumA - sumB;
        int ok = 1;
        rep(i,N) ok &= A[i] <= sumB + B1 - B[i];
        ans += ok;
    }
    cout << ans << endl;
}