#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;

ll gcd(ll a,ll b){
	if(b>a){
		ll temp=a;	a=b;	b=temp;
	}
	while(a%b!=0){
		ll temp=a%b;
		a=b;	b=temp;
	}
	return b;
}

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