import java.math.BigDecimal;
import java.util.Scanner;

public class Main {

    private static long n;

    private static long m;

    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        n = Long.parseLong(cin.next());
        m = Long.parseLong(cin.next());
        cin.close();
        calculate();
    }

    private static void calculate() {
        long target = m;
        while (target % 2 == 0) {
            target /= 2;
        }
        while (target % 5 == 0) {
            target /= 5;
        }
        if (n % target != 0) {
            System.out.println(-1);
        } else {
            String resultStr = new BigDecimal(n).divide(new BigDecimal(m)).toString();
            char[] charArray = resultStr.toCharArray();
            for (int i = charArray.length - 1; i >= 0; i--) {
                if (charArray[i] != '0') {
                    System.out.println(charArray[i]);
                    break;
                }
            }
        }
    }
}