#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<int, ll> i_ll;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };

ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

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

int main() {
	ll N, M; cin >> N >> M;
	ll d = gcd(N, M);
	N /= d; M /= d;
	int two = 0, five = 0;
	for (; M % 2 == 0; M /= 2) two++;
	for (; M % 5 == 0; M /= 5) five++;
	if (M != 1) {
		cout << -1 << endl;
		return 0;
	}
	for (; N % 10 == 0; N /= 10);
	N %= 10;
	for (; two > 0 || five > 0; two--, five--) {
		if (two <= 0) N = (N * 2) % 10;
		if (five <= 0) N = (N * 5) % 10;
	}
	cout << N << endl;
}