#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

long long GCD(long long a, long long b) {
	if (a < b) {
		swap(a, b);
	}
	long long r = a%b;
	while (r != 0)
	{
		a = b;
		b = r;
		r = a%b;
	}
	return b;
}

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