#include <cstdio>
#include <cstring>
#include <string>
#include <iostream>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <unordered_map>
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;
ll gcd(ll a, ll b){
    if(b==0) return a;
    return gcd(b, a%b);
}
int main()
{
	ll n, m;
	cin>>n>>m;
	ll d=gcd(n, m);
	n/=d, m/=d;
	ll m1=m;
	while(m1%2==0) m1/=2;
	while(m1%5==0) m1/=5;
	if(m1>1){
	    cout<<-1<<endl;
	    return 0;
	}
	while(m%10==0) m/=10;
	if(m==1){
	    while(n%10==0) n/=10;
	    cout<<n%10<<endl;
	    return 0;
	}
	if(m%2==0){
	    cout<<5<<endl;
	    return 0;
	}
	n%=10;
	while(m>1){
	    m/=5;
	    n*=2;
	    n%=10;
	}
	cout<<n<<endl;
	return 0;
}