#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000001

int main(){
	
	long long n,m;
	cin>>n>>m;
	
	long long g = gcd(n,m);
	n/=g;
	m/=g;
	
	while(m%10==0)m/=10;
	while(n%10==0)n/=10;
	long long ans;
	
	if(m==1){
		ans = n%10;
	}
	else if(m%2==0){
		int c = 0;
		while(m%2==0){
			c++;
			m/=2;
		}
		if(m==1){
			n %= 10;
			rep(i,c){
				n *= 5;
				n %= 10;
			}
			ans = n;
		}
		else{
			ans = -1;
		}
	}
	else{
		int c = 0;
		while(m%5==0){
			c++;
			m/=5;
		}
		if(m==1){
			n %= 10;
			rep(i,c){
				n *= 2;
				n %= 10;
			}
			ans = n;
		}
		else{
			ans = -1;
		}
	}
	
	cout<<ans<<endl;
	
	return 0;
}