#include <iostream>
using namespace std;

typedef long long LL;

int main(){
    LL N, M;
    cin >> N >> M;
    LL n2 = 0;
    LL n5 = 0;
    while(N % 2 == 0){ N /= 2; n2++; }
    while(N % 5 == 0){ N /= 5; n5++; }
    while(M % 2 == 0){ M /= 2; n5++; }
    while(M % 5 == 0){ M /= 5; n2++; }
    if(N % M == 0){
        LL ans = N / M % 10;
        for(int i = 0; i < n2-n5; i++){
            ans = ans * 2 % 10;
        }
        for(int i = 0; i < n5-n2; i++){
            ans = ans * 5 % 10;
        }
        cout << ans << endl;
    }else{
        cout << -1 << endl;
    }
    return 0;
}