#include <iostream>
#include <numeric>
#include <vector>

int main() {
    using namespace std;
    long long n, m;
    cin >> n >> m;
    long long g = gcd(n, m);
    n /= g;
    m /= g;
    if (n % m == 0) {
        long long q = n / m;
        while (q % 10 == 0) { q /= 10; }
        cout << q % 10 << endl;
        return 0;
    }
    while (n % 10 == 0) { n /= 10; }
    while (m % 10 == 0) { m /= 10; }
    int two = 0, five = 0;
    while (m % 2 == 0) {
        m /= 2;
        two++;
    }
    while (m % 5 == 0) {
        m /= 5;
        five++;
    }
    if (m > 1) {
        cout << -1 << endl;
    } else if (two > 0) {
        while (two--) {
            if (n % 2 > 0) {
                cout << 5 << endl;
                return 0;
            }
            n /= 2;
        }
        cout << n % 10 << endl;
    } else {
        while (five--) {
            if (n % 5 > 0) {
                n = n % 10;
                five++;
                while (five--) { n = n * 2 % 10; }
                cout << n << endl;
                return 0;
            }
            n /= 5;
        }
        cout << n % 10 << endl;
    }
}