#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <climits>
#include <map>
#include <queue>
#include <set>
#include <cstring>
#include <vector>

using namespace std;
typedef long long ll;

int main() {
  int N;
  cin >> N;
  int A[N - 1];
  int B[N - 1];
  int in_cnt = 0;
  int out_cnt = 0;
  for (int i = 0; i < N - 1; ++i) {
    cin >> A[i] >> B[i];

    in_cnt += A[i];
    out_cnt += B[i];
  }

  int ans = 0;

  for (int a = 0; a <= out_cnt; ++a) {
    int b = (in_cnt + a) - out_cnt;
    if (b < 0) continue;

    bool ok = true;

    for (int i = 0; i < N - 1; ++i) {
      int x = A[i];
      int y = B[i];
      ok &= (x <= (out_cnt + b) - y);
    }

    if (ok) {
      ++ans;
    }
  }

  cout << ans << endl;

  return 0;
}