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

#include<atcoder/all>
using namespace atcoder;

using ll=long long;

int main(){
    int N;
    cin>>N;
    int sumA=0,sumB=0;
    vector<int> A(N-1),B(N-1);
    for(int i=0;i<N-1;i++){
        cin>>A[i]>>B[i];
        sumA+=A[i],sumB+=B[i];
    }
    int ans=0;
    for(int A1=0;A1<=sumB;A1++){
        int B1=A1+sumA-sumB;
        sumA+=A1,sumB+=B1;
        if(A1<0||B1<0) continue;
        bool f=true;
        for(int i=0;i<N-1;i++){
            if(A[i]>sumB-B[i]) f=false;
        }
        if(f) ans++;
        sumA-=A1,sumB-=B1;
    }
    cout<<ans<<endl;
    return 0;
}