#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>

using namespace std;

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

int main() {
	long long n, m;

	cin >> n >> m;

	int ans;
	if (n % m == 0) {
		ans = n / m;
		while (ans % 10 == 0) {
			ans /= 10;
		}
		ans %= 10;
		cout << ans << endl;
		return 0;
	}

	n -= n / m * m;

	long long nm_gcd = gcd(m, n);
	n /= nm_gcd;
	m /= nm_gcd;

	int div2 = 0;
	int div5 = 0;
	while (m % 2 == 0) {
		m /= 2;
		div2++;
	}
	while (m % 5 == 0) {
		m /= 5;
		div5++;
	}

	if (m > 1) {
		ans = -1;
	} else {
		while (n % 10 == 0) {
			n /= 10;
		}
		ans = n % 10;

		int diff = abs(div2 - div5);
		int multiplier =  div2 > div5 ? 5 : 2;
		for (int i = 0; i < diff; i++) {
			ans = ans * multiplier % 10;
		}
	}

	cout << ans << endl;
	return 0;
}