#include <iostream>
using namespace std;

long long long_gcd(long long a, long long b) {
    if (a < b) {
        long long x = a;
        a = b; b = x;
    }
    long long r;
    for (;b > 0;){
        r = a % b;
        a = b;
        b = r;
    }
    return a;
}

int last_dig(long long a) {
    if (a == 0) {return 0;}
    for (;a % 10 == 0;) {
        a /= 10;
    }
    return a % 10;
}

int main(void) {
    long long N, M;
    cin >> N >> M;
    long long daiyaku = long_gcd(N, M);
    long long nshou = N / daiyaku;
    long long mshou = M / daiyaku;
    if (mshou == 1) {
        cout << last_dig(nshou) << endl;
        return 0;
    }
    long long digit = nshou % mshou;
    for (;mshou % 2 == 0;) {
        digit *= 5;
        mshou /= 2;

    }
    digit = last_dig(digit);
    for (;mshou % 5 == 0;) {
        digit <<= 1;
        mshou /= 5;
    }
    if (mshou > 1) {
        cout << -1 << endl;
    } else {
        digit = last_dig(digit);
        cout << digit << endl;
    }

    return 0;
}