#include <iostream> 
using namespace std;
typedef long long ll;
#define rep(i,n)	for(int i=0;i<n;i++)
int main(){
	ll n,m;	cin>>n>>m;
	ll mt=0,mf=0;
	while(m%2==0){
		m/=2;
		mt++;
	}
	while(m%5==0){
		m/=5;
		mf++;
	}
	if(n%m!=0){
		cout<<-1<<endl;
		return 0;
	}
	n/=m;
	while(mt>mf){
		n*=5;
		mf++;
	}
	while(mt<mf){
		n*=2;
		mt++;
	}
	while(n%10==0)	n/=10;
	cout<<n%10<<endl;
	return 0;
}