#include <iostream>
using namespace std;
typedef unsigned long long ull;

ull gcd(ull a, ull b){
    if(b == 0)return a;
    return gcd(b, a % b);
}

int main(){
    ull N, M;
    cin >> N >> M;
    
    ull g = gcd(N, M);
    N /= g;
    M /= g;
    
    if(M == 1){
        while(N % 10 == 0){
            N /= 10;
        }
    
        cout << N % 10 << endl;
        return 0;
    }
    
    int e2 = 0, e5 = 0;
    while(M % 2 == 0){
        M /= 2;
        ++e2;
    }
    while(M % 5 == 0){
        M /= 5;
        ++e5;
    }
    
    if(M != 1){
        cout << -1 << endl;
        return 0;
    }
    
    int maxi = max(e2, e5);
    e2 = maxi - e2;
    e5 = maxi - e5;
    
    N %= 10;
    while(e2--){
        N = (N * 2) % 10;
    }
    while(e5--){
        N = (N * 5) % 10;
    }
    
    cout << N << endl;
    
    return 0;
}