代码：

#include<iostream>

using namespace std;

typedef long long LL;

const int N = 23;

int n;
LL a[N], b[N], m, y[N], x;

LL exgcd(LL a, LL b, LL &x, LL &y){
	if(b == 0){
		x = 1, y = 0;
		return a;
	}
	LL tmp = exgcd(b, a % b, x, y);
	LL t = x;
	x = y;
	y = t - a / b * y;
	return tmp;
}

int main(){
	
	cin >> n;
	m = 1;
	for(int i = 1; i <= n; i ++){
		cin >> a[i] >> b[i];
		m *= a[i]; 
	}
	for(int i = 1; i <= n; i ++){
		LL p = 0, q = 0;//p是逆元 
		LL now = m / a[i];
		exgcd(abs(now), abs(a[i]), p, q);
		p = (p % m + m) % m;
		x = ((x + now * p * b[i]) % m + m) % m; 
	}
	x = (x + m) % m;
	cout << x;
	return 0;
}