#include <iostream>
#include <vector>
#include <algorithm>
#include <string>

#define REP(i, a, b) for (int i = int(a); i < int(b); i++)
#define dump(val) cerr << __LINE__ << ":\t" << #val << " = " << (val) << endl

using namespace std;

typedef long long int lli;

template<typename T>
vector<T> make_v(size_t a, T b) {
    return vector<T>(a, b);
}

template<typename... Ts>
auto make_v(size_t a, Ts... ts) {
    return vector<decltype(make_v(ts...))>(a, make_v(ts...));
}

lli gcd(lli a, lli b) {
    if (b == 0) {
        return a;
    } else {
        return gcd(b, a % b);
    }
}

int main() {
    lli N, M;
    cin >> N >> M;
    lli g = gcd(N, M);
    N /= g;
    M /= g;
    if (M == 1) {
        while (N % 10 == 0) {
            N /= 10;
        }
        cout << N % 10 << endl;
    } else {
        int two = 0, five = 0;
        while (M % 2 == 0) {
            two++;
            M /= 2;
        }
        while (M % 5 == 0) {
            five++;
            M /= 5;
        }
        if (M != 1) {
            cout << -1 << endl;
        } else {
            if (two < five) {
                N %= 10;
                cout << ((1LL << (five - two)) * N) % 10 << endl;
            } else if (two > five) {
                cout << 5 << endl;
            } else {
                cout << N % 10 << endl;
            }
        }
    }
    return 0;
}