#include <iostream>
#include <string>
using namespace std;

int main() {
	long long n, m;
	cin >> n >> m;

	long long divided = n;
	long long mod = m;
	long long gcd = 0;

	while (true) {
		long long surplus = divided % mod;
		if (surplus == 0) {
			gcd = mod;
			break;
		}
		else {
			divided = mod;
			mod = surplus;
		}
	}

	long long numerator = n / gcd;
	while (numerator % 10 == 0) {
		numerator /= 10;
	}
	numerator %= 10;

	long long denominator = m / gcd;
	int pf2 = 0;
	int pf5 = 0;
	while (denominator > 1) {
		if (denominator % 2 == 0) {
			denominator /= 2;
			pf2++;
		}
		else if (denominator % 5 == 0) {
			denominator /= 5;
			pf5++;
		}
		else {
			break;
		}
	}

	if (denominator > 1) {
		cout << -1 << endl;
		return 0;
	}

	while (pf2 > pf5) {
		numerator = (numerator * 5) % 10;
		pf5++;
	}

	while (pf5 > pf2) {
		numerator = (numerator * 2) % 10;
		pf2++;
	}

	cout << numerator << endl;

	return 0;
}