#include <iostream>
#include <numeric>

using lint = long long;

void solve() {
    lint n, m;
    std::cin >> n >> m;

    auto g = std::gcd(n, m);
    n /= g, m /= g;

    while (m % 10 == 0) m /= 10;
    while (n % 10 == 0) n /= 10;

    n %= 10;
    while (m % 2 == 0) {
        m /= 2;
        (n *= 5) %= 10;
    }
    while (m % 5 == 0) {
        m /= 5;
        (n *= 2) %= 10;
    }

    std::cout << (m == 1 ? n : -1) << "\n";
}

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

    solve();

    return 0;
}