#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <chrono>
#define _USE_MATH_DEFINES
#include <cmath>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iostream>
#include <iterator>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
using namespace std;

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

const int INF = 0x3f3f3f3f;
const long long LINF = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-8;
const int MOD = 1000000007; // 998244353;
const int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
/*-------------------------------------------------*/
int main() {
  cin.tie(nullptr); ios::sync_with_stdio(false);
  // freopen("input.txt", "r", stdin);

  int n; cin >> n;
  vector<int> a(n), b(n);
  int out = 0, diff = 0;
  FOR(i, 1, n) {
    cin >> a[i] >> b[i];
    out += b[i];
    diff += a[i] - b[i];
  }
  int ans = 0;
  REP(i, out + 1) {
    a[0] = i;
    b[0] = i + diff;
    if (b[0] < 0) continue;
    int now_out = out + b[0];
    bool ok = true;
    REP(j, n) {
      if (now_out - b[j] < a[j]) ok = false;
    }
    if (ok) ++ans;
  }
  cout << ans << '\n';
  return 0;
}