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

long long gcd(long long a, long long b){
	if (b == 0) return a;
	return gcd(b, a%b);
}

int main() {
	long long N, M;
	cin >> N >> M;
	long long g = gcd(N, M);
	N /= g;
	M /= g;
	while (N % 10 == 0) N /= 10;
	N %= 10;
	while (M % 5 == 0){
		M /= 5;
		N *= 2;
		N %= 10;
	}
	while (M % 2 == 0){
		M /= 2;
		N *= 5;
		N %= 10;
	}
	if (M == 1) cout << N << endl;
	else cout << -1 << endl;
}