#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, X, cnt2=0, cnt5=0, s;
    cin >> N >> M;
    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 % 2 == 0 && cnt2 > 0){
        cnt2--;
        N /= 2;
    }
    while(N % 5 == 0 && cnt5 > 0){ 
        cnt5--;
        N /= 5;
    }

    if (cnt2 > 0) s = 5;
    else s = N % 10;
    
    while(cnt5 > 0){
        s = ((s * 10) / 5) % 10;
        cnt5--;
    }

    cout << s << endl;

    return 0;
}