void Extend_GCD(LL a, LL b, LL &d, LL &x, LL &y)
{
    if (!b) d = a, x = 1, y = 0;
    else { Extend_GCD(b, a%b, d, y, x); y -= x * (a/b); }
}
 
int main()
{
    //ROP;
    int n;
    while (~scanf("%d", &n))
    {
        LL a1, r1;
        scanf("%lld%lld", &a1, &r1);
        bool flag = false;
        if (n == 1) r1 = a1+r1;
        for (int i = 0; i < n-1; i++)
        {
            LL a2, r2;
            scanf("%lld%lld", &a2, &r2);
            if (flag) continue;
            LL x, y, A = a1, B = a2, C = r2 - r1, g;
            Extend_GCD(A, B, g, x, y);
            if (C % g)
            {
                flag = true;
                continue;
            }
            x = C / g * x;
            x = x - (x*g/B) * (B/g);
            if (x < 0) x += B / g;
            r1 = x*a1 + r1;
            a1 = a1 / g * a2;
        }
        if (flag) puts("-1");
        else printf("%lld\n", r1);
    }
    return 0;
}