#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

using ll = long long;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    ll N, M;
    cin >> N >> M;
    ll g = gcd(N, M);
    M /= g;
    while(M % 10 == 0)  M /= 10;
    ll X = M;
    while(X % 2 == 0)   X /= 2;
    while(X % 5 == 0)   X /= 5;
    if(X != 1){
        cout << -1 << endl;
        return 0;
    }
    N /= g;
    while(N % 10 == 0)  N /= 10;
    N %= 10;
    while(M % 2 == 0){
        (N *= 5) %= 10;
        M /= 2;
    }
    while(M % 5 == 0){
        (N *= 2) %= 10;
        M /= 5;
    }
    cout << N << endl;
    
    return 0;
}