#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
#include <map>

using namespace std;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int N;
    long A[40], B[40];
    cin >> N;
    long min_sum = -1e+8, max_sum = 1e+8;
    long sum_A = 0, sum_B = 0;
    for(int i = 0; i < N-1; i++){
        cin >> A[i] >> B[i];
        min_sum = max(min_sum, 2*(A[i]+B[i]));
        sum_A += A[i];
        sum_B += B[i];
    }
    max_sum = sum_A*2+sum_B*2;
    long diff = abs(sum_A-sum_B);
    long ans = 0;
    //cout << diff << endl;
    //cout << min_sum << ' ' << max_sum << endl;
    for(int i = 0; 2*i+diff+sum_A+sum_B <= max_sum; i++){
        if(i*2+diff+sum_A+sum_B < min_sum) continue;
        ans++;
    }
    cout << ans << endl;
}