#include <bits/stdc++.h>
using namespace std;
using ll = long long;
ll gcd(ll a, ll b) {
    while (b) {
        ll c = b;
        b = a % b;
        a = c;
    }
    return a;
}

int main() {
    ll N, M;
    cin >> N >> M;

    ll G = gcd(N, M);
    N /= G;
    M /= G;

    while (N % 10 == 0)
        N /= 10;

    while (M % 10 == 0)
        M /= 10;
    while (M % 2 == 0) {
        M /= 2;
        N *= 5;
        if (N % 10 == 0)
            N /= 10;
        N %= 10;
    }
    while (M % 5 == 0) {
        M /= 5;
        N *= 2;
        if (N % 10 == 0)
            N /= 10;
        N %= 10;
    }

    if (M != 1) N = -1;
    cout << N << endl;
}