#include<iostream>
#include<algorithm>
#include<string>
using namespace std;
#define LL long long
int main(void){
	LL N, M;
	cin >> N >> M;
	if (N%M == 0){
		string str = to_string(N / M);
		for (int i = (int)str.size() - 1; i >= 0; i--){
			if (str[i] != '0'){
				cout << str[i];
				break;
			}
		}
	}
	else{
		int nx, ny;
		nx = ny = 0;
		while (N % 2 == 0)N /= 2, nx++;

		while (N % 5 == 0)N /= 5, ny++;

		while (M % 2 == 0)M /= 2, nx--;

		while (M % 5 == 0)M /= 5, ny--;
	//	cout << nx << " " << ny << endl;
		if (N%M){
			cout << -1 << endl;
			return 0;
		}
		while (nx < 0 || ny < 0)nx++, ny++;
		LL res = N / M;
		res %= 10;
		LL tmp = 1;
		while (nx--){
			tmp = (tmp * 2) % 10;
		}
		if (ny>0)tmp *= 5;
		res = (res*tmp) % 10;
		cout << res << endl;
	}
	return 0;
}