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

int main() {
  int n;
  cin>>n;
  int as[n-1], bs[n-1];
  int a_sum = 0, b_sum = 0;
  for (int i=0; i<n-1; i++) {
    cin>>as[i]>>bs[i];
    a_sum += as[i];
    b_sum += bs[i];
  }
  int min_a1 = 0, min_b1 = 0;
  if (a_sum > b_sum) {
    min_b1 = a_sum - b_sum;
  } else if (a_sum < b_sum) {
    min_a1 = b_sum - a_sum;
  }
  for (int i=0; i<n-1; i++) {
    if (as[i] > b_sum - bs[i]) {
      min_b1 = max(as[i] - (b_sum - bs[i]), min_b1);
    }
    if (bs[i] > a_sum - as[i]) {
      min_a1 = max(bs[i] - (a_sum - as[i]), min_a1);
    }
  }

  int cnt = 0;
  for (int i=min_a1; i<=b_sum; i++) {
    int b = a_sum - b_sum + i;
    if (b >= min_b1) {
      ++cnt;
    }
  }
  cout<<cnt<<endl;
}