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

int main(){
    int N, A[36], B[36];
    cin >> N;
    int as = 0, bs = 0;
    for(int i=0; i<N-1; i++){
        cin >> A[i] >> B[i];
        as += A[i];
        bs += B[i];
    }
    int amin = max(0, bs-as);
    for(int i=0; i<N-1; i++) amin = max(amin, A[i] + B[i] - as);
    int amax = bs;
    int ans = max(0, amax-amin+1);
    cout << ans << endl;
}