#include <iostream>
#include <vector>
#include <cstring>
#include <string>
#include <algorithm>
#include <iomanip>
#include <cmath>
#include <cassert>
using namespace std;

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


int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	ll N, M;
	cin >> N >> M;

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

	if(M == 1) {
		while(N % 10 == 0) N /= 10;
		cout << N % 10 << endl;
		return 0;
	}

	int t = 0, f = 0;
	ll m = M;
	while(m % 2 == 0) {
		m /= 2;
		t++;
	}
	while(m % 5 == 0) {
		m /= 5;
		f++;
	}

	if(m != 1) {
		cout << -1 << endl;
		return 0;
	}

	if(t > f) {
		for(int i = 0; i < t - f; i++) {
			N *= 5;
			N %= 1000000;
			while(N % 10 == 0) N /= 10;
		}
	}
	else {
		for(int i = 0; i < f - t; i++) {
			N *= 2;
			N %= 1000000;
			while(N % 10 == 0) N /= 10;
		}
	}

	cout << N % 10 << endl;

}