#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
void exgcd(LL a, LL b, LL &d, LL &x, LL &y) 
{
    if(b==0)d=a, x=1, y=0;
    else
    {
        exgcd(b, a%b, d, y, x);
        y-=(a/b)*x;
    }
}
int main()
{
    LL a1, b1, a2, b2, A, B, X, Y, K, d;
    int n;
    while(scanf("%d", &n)!=EOF)
    {
        bool bk = true; 
        scanf("%lld%lld", &a1, &b1);
        for(int i=2; i<=n; i++) 
        {
            scanf("%lld%lld", &a2, &b2);
            A = a1; B = a2; K = b2 - b1;
            exgcd(A, B, d, X, Y);
            if(K % d != 0) bk = false;
            LL dx = abs(B/d), dy = abs(A/d);
            X = X * (K/d);
            X = (X % dx + dx) % dx;
            b1 = a1 * X + b1;
            a1 = a1 / d * a2;
        }
        if(bk == false) printf("-1\n");
        else printf("%lld\n", b1);
    }
    return 0;
}