#include<bits/stdc++.h>
using namespace std;
#define rep(i,N) for(int (i)=0;(i) < (N); (i)++)
#define all(V) V.begin(), V.end()
using i64 = int_fast64_t;
using P = pair<i64,i64>;

int main(){
    int N;
    cin >> N;
    i64 in = 0, out = 0;
    vector<i64> A(N), B(N); 
    rep(i,N-1){
        cin >> A[i+1] >> B[i+1];
        in += A[i+1];
        out += B[i+1];
    }

    i64 ans = 0;
    for(int i = 0; i <= in; i++){
        int a = out + i - in;
        if(0 <= a && a <= out){
            bool ok = true;
            for(int k = 1; k < N; k++){
                if(0 > A[k] || A[k] > out+i-B[k]) ok = false;
                if(0 > B[k] || B[k] > in+a-A[k]) ok = false;
            }
            if(ok) ans++;
        } 
    }
    cout << ans << endl;
}