#include <bits/stdc++.h>
using namespace std;
using i64 = int64_t;
using vi = vector<i64>;
using vvi = vector<vi>;

int main() {
    i64 n, m;
    cin >> n >> m;
    i64 g = __gcd(n, m);

    n /= g;
    m /= g;

    if (n % m == 0) {
        i64 k = n / m;
        while (k % 10 == 0) {
            k /= 10;
        }
        cout << k % 10 << endl;
        return 0;
    }

    n %= m;
    i64 M = m;
    int t = 0, f = 0;
    while (M % 2 == 0) {
        M /= 2;
        t++;
    }
    while (M % 5 == 0) {
        M /= 5;
        f++;
    }
    if (M != 1) {
        cout << -1 << endl;
        return 0;
    }

    if (t < f) {
        n %= 10;
        for (int i = 0; i < f - t; i++) {
            n *= 2;
            n %= 10;
        }
        cout << n << endl;
    } else {
        n %= 10;
        for (int i = 0; i < t - f; i++) {
            n *= 5;
            n %= 10;
        }
        cout << n << endl;
    }
}