#include <bits/stdc++.h>
using namespace std;
using lint = long long;
template<class T = int> using V = vector<T>;
template<class T = int> using VV = V< V<T> >;

int main() {
  cin.tie(nullptr); ios::sync_with_stdio(false);
  int n; cin >> n;
  if (n == 2) {
    return cout << 1 << '\n', 0;
  }
  int a = 0, b = 0;
  for (int _ = 0; _ < n - 1; ++_) {
    int x, y; cin >> x >> y;
    a += x;
    b += y;
  }
  int res = 0;
  for (int i = 0; i < 1e7; ++i) {
    int x = i, y = a + x - b;
    if (x > b or y > a) continue;
    if (x < 0 or y < 0) continue;
    ++res;
  }
  cout << res << '\n';
}