#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;
  V<> a(n), b(n);
  for (int i = 1; i < n; ++i) {
    cin >> a[i] >> b[i];
  }
  int sa = accumulate(begin(a), end(a), 0);
  int sb = accumulate(begin(b), end(b), 0);
  int res = 0;
  for (a[0] = 0; a[0] <= sb; ++a[0]) {
    b[0] = a[0] + sa - sb;
    if (b[0] < 0 or b[0] > sa) continue;
    int ta = accumulate(begin(a), end(a), 0);
    int tb = accumulate(begin(b), end(b), 0);
    bool ok = true;
    for (int i = 0; i < n; ++i) {
      if (a[i] > tb - b[i]) {
        ok = false;
        break;
      }
      if (b[i] > ta - a[i]) {
        ok = false;
        break;
      }
    }
    res += ok;
  }
  cout << res << '\n';
}