#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;
  }
  V<> x(n - 1), y (n - 1);
  int a = 0, b = 0;
  for (int i = 0; i < n - 1; ++i) {
    cin >> x[i] >> y[i];
    a += x[i];
    b += y[i];
  }
  int p = 0, q = 0;
  for (int i = 0; i < n - 1; ++i) {
    int t = x[i];
    for (int j = 0; j < n - 1; ++j) if (j != i) {
      t -= y[j];
    }
    p += max(t, 0);
    t = y[i];
    for (int j = 0; j < n - 1; ++j) if (j != i) {
      t -= x[j];
    }
    q += max(t, 0);
  }
  int res = 0;
  for (int i = -1e8; i < 1e8; ++i) {
    int x = i, y = a + x - b;
    if (x > b or y > a) continue;
    if (x < p or y < q) continue;
    ++res;
  }
  cout << res << '\n';
}