#include <bits/stdc++.h>
using namespace std;
using ll = long long;

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

int main(void) {
	ll N, M;
	cin >> N >> M;
	
	ll d = gcd(N, M);
	N /= d, M /= d;
	
	while(N % 10 == 0) N /= 10;
	while(M % 10 == 0) M /= 10;
	
	int ans = N % 10;
	ll T = M;
	while(T % 2 == 0) {
		T /= 2;
		ans = 5;
	}
	while(T % 5 == 0) {
		T /= 5;
		ans = ans * 2 % 10;
	}
	
	cout << (T == 1 ? ans : -1) << endl;
	return 0;
}