#include <iostream>
#include <string>
#include <map>
using namespace std;

typedef long long ll;

ll GCD(ll a, ll b) {
    if (b == 0) return a;
    else return GCD(b, a % b);
}

map<ll, int> PrimeFactorization(ll n) {
    map<ll, int> res;
    for (ll i = 2; i * i <= n; i++) {
        while (n % i == 0) {
            res[i]++;
            n /= i;
        }
    }
    if (n != 1) res[n]++;
    return res;
}

int main() {
    ll N, M, gcd;
    cin >> N >> M;

    gcd = GCD(N, M);
    N /= gcd;
    M /= gcd;

    map<ll, int> factors = PrimeFactorization(M);
    int exp2 = 0, exp5 = 0;
    for (auto it = factors.begin(); it != factors.end(); it++) {
        if (it->first == 2) {
            exp2 = it->second;
        } else if (it->first == 5) {
            exp5 = it->second;
        } else {
            cout << -1 << endl;
            return 0;
        }
    }
    // 確実に下一桁が0以外の数字にするために
    while (N % 10 == 0) {
        N /= 10;
    }
    for (int i = 0; i < max(exp2, exp5) - exp2; i++) {
        N = (N * 2) % 10;
    }
    for (int i = 0; i < max(exp2, exp5) - exp5; i++) {
        N = (N * 5) % 10;
    }
    cout << (N % 10) << endl;

    return 0;
}