using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Diagnostics;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using Enu = System.Linq.Enumerable;

class Program
{
    void Solve()
    {
        long Y = reader.Long(), X = reader.Long();
        long gcd = GCD(Y, X);
        Y /= gcd;
        X /= gcd;
        long t = X, p2 = 0, p5 = 0;
        while (t % 2 == 0) { t /= 2; p2++; }
        while (t % 5 == 0) { t /= 5; p5++; }
        if (t != 1) { Console.WriteLine(-1); return; }
        while (Y % 10 == 0) Y /= 10;
        Y %= 10;
        for (int i = 0; i < p5 - p2; i++) Y = (Y * 2) % 10;
        for (int i = 0; i < p2 - p5; i++) Y = (Y * 5) % 10;
        Console.WriteLine(Y);
    }

    static long GCD(long a, long b) { while (b != 0) { long r = a % b; a = b; b = r; } return a; }

    Reader reader = new Reader(Console.In);
    static void Main() { new Program().Solve(); }
}

class Reader
{
    private readonly TextReader reader;
    private readonly char[] separator = { ' ' };
    private readonly StringSplitOptions removeOp = StringSplitOptions.RemoveEmptyEntries;
    private string[] A = new string[0];
    private int i;

    public Reader(TextReader r) { reader = r; }
    public bool HasNext() { return Enqueue(); }
    public string String() { return Dequeue(); }
    public int Int() { return int.Parse(Dequeue()); }
    public long Long() { return long.Parse(Dequeue()); }
    public double Double() { return double.Parse(Dequeue()); }
    public int[] IntLine() { var s = Line(); return s == "" ? new int[0] : Array.ConvertAll(Split(s), int.Parse); }
    public int[] IntArray(int N) { return Enu.Range(0, N).Select(i => Int()).ToArray(); }
    public int[][] IntGrid(int H) { return Enu.Range(0, H).Select(i => IntLine()).ToArray(); }
    public string[] StringArray(int N) { return Enu.Range(0, N).Select(i => Line()).ToArray(); }
    public string Line() { return reader.ReadLine().Trim(); }
    private string[] Split(string s) { return s.Split(separator, removeOp); }
    private bool Enqueue()
    {
        if (i < A.Length) return true;
        string line = reader.ReadLine();
        if (line == null) return false;
        if (line == "") return Enqueue();
        A = Split(line);
        i = 0;
        return true;
    }
    private string Dequeue() { Enqueue(); return A[i++]; }
}