#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;
    i64 a,b;
    rep(i,N-1){
        cin >> a >> b;
        in += a;
        out += b;
    }

    i64 ans = 0;
    for(int i = 0; i <= in; i++){
        a = out + i - in;
        if(0 <= a && a <= out) ans++; 
    }
    cout << ans << endl;
}