#include <bits/stdc++.h>
using namespace std;

#define REP(i, n) for(int (i) = 0; (i) < (n); (i)++)
#define MAX(a, b) ((a) > (b) ? (a) : (b))
#define MIN(a, b) ((a) < (b) ? (a) : (b))

typedef long long ll;

int main(void){
	int n;
	cin >> n;

	int sum[2] = {}, a[n] = {}, b[n] = {};
	REP(i, n-1){
		cin >> a[i+1] >> b[i+1];
		sum[0] += a[i+1];
		sum[1] += b[i+1];
	}

	int ans = 0;
	REP(i, MIN(sum[0], sum[1])+1){
		a[0] = sum[1]-i; b[0] = sum[0]-i;
		REP(j, n){
			if(a[j] > sum[1]+b[0]-b[j]){
				cout << ans << endl;
				return 0;
			}
		}
		ans++;
	}

	cout << ans << endl;

	return 0;
}