#include <bits/stdc++.h>

using namespace std;

typedef pair<int,int> P;
typedef pair<int,pair<int,int>> PP;
typedef long long ll;

const double EPS = 1e-8;
const int INF = 1e9;
const int MOD = 1e9+7;

int dy[] = {0,1,0,-1};
int dx[] = {1,0,-1,0};

int main(void) {
	long long n,m,mm;
	cin >> n >> m;
	ll r = __gcd(n,m);
	m /= r;n /= r;
	ll a=0,b=0;
	while(m%2==0){m/=2;a++;}
	while(m%5==0){m/=5;b++;}
	if(m != 1){
		cout << -1 << endl;
		exit(0);
	}

	
	while(n%10==0)n/=10;
	n %= 10;
	while(a > b){b++;n=(n*5)%10;}
	while(b > a){a++;n=(n*2)%10;}

	cout << n << endl;
	return 0;
}