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

typedef long long ll;

const int N = 1e5 + 5;

int n;
int a[N], m[N];

ll mul(ll a, ll b, ll m) {
	int res = 0;
	for (; b; b >>= 1) {
		if (b & 1) res = (res + a) % m;
		a = (a + a) % m;
	}
	return res;
}

ll exgcd(ll a, ll b, ll &x, ll &y) {
	if (b == 0) {
		x = 1, y = 0;
		return a;
	}
	ll d = exgcd(b, a % b, x, y);
	int z = x;
	x = y, y = z - (a / b) * y;
	return d;
}

ll excrt() {
	ll x, y;
	ll m1 = m[1], a1 = a[1];
	ll ans = 0;
	for (int i = 2; i <= n; i++) {
		ll a2 = a[i], m2 = m[i];
		ll a = m1, b = m2, c = (a2 - a1 % m2 + m2) % m2;
		ll d = exgcd(a, b, x, y);
		if (c % d != 0) return -1;
		x = mul(x, c / d, b / d);
		ans = a1 + x * m1;
		m1 = m2 / d * m1;
		ans = (ans % m1 + m1) % m1;
		a1 = ans;
	}
	return ans;
}

int main() {
	scanf("%d", &n);
	for (int i = 1; i <= n; i++) scanf("%d%d", &m[i], &a[i]);
	printf("%lld", excrt());
	return 0;
}