#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n;
  cin >> n;

  vector<int> a(n), b(n);
  int asum = 0, bsum = 0;
  FOR (i, 1, n) {
    cin >> a[i] >> b[i];
    asum += a[i];
    bsum += b[i];
  }
  
  int ret = 0;
  for (int x = 0; x <= 37 * 10000; x++) {
    a[0] = x;
    b[0] = x + asum - bsum;

    bool ck = true;
    ck &= b[0] >= 0;

    int sum = x + asum;
    REP (i, n)
      ck &= a[i] <= sum - b[i];

    if (ck)
      ++ret;
  }

  cout << ret << endl;
  
  return 0;
}