易得：

#include<bits/stdc++.h>
#define LL long long

using namespace std;

void exgcd(LL a, LL b, LL &g, LL &x, LL &y)
{
	if (b == 0) g = a, x = 1, y = 0;
	else exgcd(b, a%b, g, y, x), y -= (a/b) * x;
}

LL inv(LL a, LL mo)
{
	LL g, x, y;
	exgcd(a, mo, g, x, y);
	return (x + mo) % mo;
}

int n;

int main ()
{
	cin >> n;
	LL A = 1, B = 0;
	for (int i = 1; i <= n; i++) 
	{
		LL a, b;
		cin >> a >> b;
		LL g, x, y;
		exgcd(a, A, g, x, y);
		A = (a / g) * A;
		B = ((B-b) / g * x % A * a % A + b + A) % A;
	}
	cout << B << endl;
}
/*
x % a1 = b1;
x % a2 = b2;

==>
a1 * c1 - a2 * c2 = b2 - b1;

c1 = x, x2 = -y;

c1 * a1 + b1 = x;
(kx * a + k * b y)% A = B;

*/

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

int n;

void exgcd(int a, int b, int &g, int &x, int &y) {
	// ax + by = gcd(a, b)
	if (b == 0) {
		g = a, x = 1, y = 0;
	} else {
		exgcd(b, a % b, g, y, x);
		y -= a / b * x;
	}
}

int lcm(int x, int y) { return x / __gcd(x, y) * y; }

void mgr(int a, int b, int m1, int m2, int &B, int &m) {
	// x = a (mod m1) + x = b (mod m2) => x = m1*p+a1 (mod lcm(m1, m2))
	// exgcd: m1*p-m2*q = b - a
	m = lcm(m1, m2);
	int g, x, y;
	exgcd(m1, m2, g, x, y);
	x = (x % m * ((((b - a) / g) + m) % m) + m) % m;
	B = (((m1 % m * x % m + a % m) % m) + m) % m;
}

bool chk(int a1, int a2, int m1, int m2) {
	// when (a2 - a1) % gcd(m1, m2) != 0 return false
	// else return true;
	if ((a2 - a1) % __gcd(m1, m2) != 0) return false;
	return true;
}

signed main() {
	cin >> n;
	int B, MOD;
    int b, mod;
	cin >> MOD >> B;
	for (int i = 1; i < n; ++i) {
		cin >> mod >> b;
		// if (!chk(b, baseB, a, baseA)) {
		// 	cout << -1 << endl;
		// 	return 0;
		// }
        // mgr(B, b, MOD, mod, B, MOD);
		mgr(b, B, mod, MOD, B, MOD);
	}
	cout << B % MOD << endl;
	return 0;
}