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

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

int n, a1, m1, a2, m2, k1, k2;
signed main() {
    cin >> n >> a1 >> m1;
    n--;
    while (n--) {
        cin >> a2 >> m2;

        int d = exgcd(a1, -a2, k1, k2);
        if ((m2 - m1) % d) {
            cout << -1 << endl;
            exit(0);
        }

        k1 *= (m2 - m1) / d;

        int t = abs(a2 / d);
        k1 = (k1 % t + t) % t;

        m1 = k1 * a1 + m1;
        a1 = abs(a1 / d * a2);
    }

    cout << (m1 % a1 + a1) % a1 << endl;
}