#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>

using namespace std;

int main(){

    long long N, M, g, X, cnt2=0, cnt5=0, s;
    cin >> N >> M;
    g = gcd(N, M);
    N /= g; M /= g;
    if (N % M == 0){
        X = N/M;
        while(X != 0){
            if (X % 10 != 0){
                cout << X % 10 << endl;
                return 0;
            }
            X /= 10;
        }
    }

    while(M % 2 == 0){
        cnt2++;
        M /= 2;
    }
    while(M % 5 == 0){
        cnt5++;
        M /= 5;
    }

    if (M != 1){
        cout << -1 << endl;
        return 0;
    }

    while (N % 10 == 0) N /= 10;
    s = N % 10;
    
    while(cnt5 > cnt2){
        s = s*2 % 10;
        cnt2++;
    }
    while(cnt2 > cnt5){
        s = s*5 % 10;
        cnt5++;
    }

    cout << s << endl;

    return 0;
}