#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
#define all(a) (a).begin(),(a).end()
#define dunk(a) cout << (a) << endl
using namespace std;
typedef long long ll;

signed int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	int n;
	cin >> n;
	vector<int> a(n - 1);
	vector<int> b(n - 1);
	rep(i, n - 1) cin >> a[i] >> b[i];

	int res1 = accumulate(all(a), 0);
	int res2 = accumulate(all(b), 0);

	int ans = 0;
	rep(i, res2 + 1) {
		int c = (res1 + i) - res2;
		bool elf = (c >= 0) ? true : false;
		rep(j, n - 1) {
			if (a[j] > (c + res2) - b[j]) {
				elf = false;
			}
		}
		ans += elf;
	}
	dunk(ans);
	return 0;
}