#include <iostream>
#include <numeric>
#include <unordered_map>

long long solve(long long N, long long M) {
    long long g = std::gcd(M, N);
    N /= g;
    M /= g;
    N %= 10;

    std::unordered_map<int, int> ct = {{2, 0},
                                       {5, 0}};
    for (const auto &x: {2, 5}) {
        while (M % x == 0) {
            ct.at(x)++;
            M /= x;
        }
    }
    if (M != 1) { return -1; }

    if (ct.at(2) <= ct.at(5)) {
        for (int i = 0; i < ct.at(5) - ct.at(2); i++) {
            N *= 2;
            N %= 10;
        }
    } else {
        for (int i = 0; i < ct.at(2) - ct.at(5); i++) {
            N *= 5;
            N %= 10;
        }
    }
    N %= 10;
    return N;
}

int main() {
    long long N, M;
    std::cin >> N;
    std::cin >> M;
    std::cout << solve(N, M) << std::endl;
}