#include <iostream>
#include <stdio.h>
#define llint long long

using namespace std;

int n;
int a, b;

int main(void)
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	cin >> n;
	int x, y;
	for(int i = 2; i <= n; i++){
		cin >> x >> y;
		a += x, b += y;
	}
	if(n == 2){
		cout << 1 << endl;
		return 0;
	}
	if(a <= b) cout << b - max(b-a, 0) + 1 << endl;
	else cout << a - max(a-b, 0) + 1 << endl;
	
	return 0;
}