#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
const int N = 40;
int n;
int a[N], b[N];
bool ok (int x) {
  a[0] = x;
  b[0] = 0;
  for (int i = 0; i < n; i++) {
    b[0] += a[i];
  }
  for (int i = 1; i < n; i++) {
    b[0] -= b[i];
  }
  if (b[0] < 0) return false;
  int sum_a = 0, sum_b = 0;
  for (int i = 0; i < n; i++) {
    sum_a += a[i];
    sum_b += b[i];
  }
  for (int i = 0; i < n; i++) {
    if (sum_a - a[i] < b[i]) return false;
    if (sum_b - b[i] < a[i]) return false;
  }
  return true;
}
signed main() {
  ios::sync_with_stdio(false); cin.tie(0);
  cin >> n;
  for (int i = 1; i < n; i++) {
    cin >> a[i] >> b[i];
  }
  int ans = 0;
  for (int i = 0; i <= 404040; i++) {
    if (ok(i)) ans++;
  }
  cout << ans << '\n';
  return 0;
}