import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        long n = sc.nextLong();
        long m = sc.nextLong();
        long gcd = getGCD(n, m);
        m /= gcd;
        n /= gcd;
        while (m % 2 == 0) {
            if (n % 10 > 0) {
                n *= 10;
            }
            m /= 2;
            n /= 2;
        }
        while (m % 5 == 0) {
            if (n % 10 > 0) {
                n *= 10;
            }
            m /= 5;
            n /= 5;
        }
        if (m > 1) {
            System.out.println(-1);
            return;
        }
        while (n % 10 == 0) {
            n /= 10;
        }
        System.out.println(n % 10);
    }
    
    static long getGCD(long x, long y) {
        if (x % y == 0) {
            return y;
        } else {
            return getGCD(y, x % y);
        }
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String next() throws Exception {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}