#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cmath>
#include <stdio.h>
#include <queue>
#include <deque>
#include <cstdio>
#include <set>
#include <map>
#include <bitset>
#include <stack>
#include <cctype>
using namespace std;
long long gcd(long long a, long long b) {
    if (a % b == 0) {
        return (b);
    }
    else {
        return (gcd(b, a % b));
    }
}
int main(){
    long long n, m;
    cin >> n >> m;
    long long g = gcd(n, m);
    n /= g;
    m /= g;
    if (m == 1) {
        string s = to_string(n);
        for (int i = s.size() - 1; i >= 0; i--) {
            if (s[i] != '0') {
                cout << s[i] << endl;
                return 0;
            }
        }
    }
    else {
        long long m1 = m;
        long long n1 = n % 10;
        int co = 0, co1 = 0;
        while (m1 % 2 == 0) {
            m1 /= 2;
            co++;
        }
        while (m1 % 5 == 0) {
            m1 /= 5;
            co1++;
        }
        if (m1 != 1) {
            cout << "-1" << endl;
        }
        else {
            if (co >= co1) {
                for (int i = 0; i < co - co1; i++) {
                    n1 *= 5;
                    n1 %= 10;
                }
            }
            else {
                for (int i = 0; i < co1 - co; i++) {
                    n1 *= 2;
                    n1 %= 10;
                }
            }
            cout << n1 << endl;
        }
    }
}