using System;
using System.Collections.Generic;
using System.Text;
class Program
{
    public void Proc()
    {
        Reader.IsDebug = false;
        long bunsi = long.Parse(Reader.ReadLine());
        long bunbo = long.Parse(Reader.ReadLine());

        long kouyakusu = this.GetKouyaku(bunbo, bunsi);
        bunsi = bunsi / kouyakusu;
        bunbo = bunbo / kouyakusu;

        long tempBunbo = bunbo;

        int div2 = 0;
        int div5 = 0;
        while (tempBunbo % 2 == 0)
        {
            div2++;
            tempBunbo = tempBunbo / 2;
        }
        while (tempBunbo % 5 == 0)
        {
            div5++;
            tempBunbo = tempBunbo / 5;
        }
        int tmp = Math.Min(div2, div5);
        div2 -= tmp;
        div5 -= tmp;
        long ans = -1;
        if (tempBunbo == 1)
        {
            while (bunsi % 10 == 0)
            {
                bunsi /= 10;
            }
            for (int i = 0; i < div2; i++)
            {
                bunsi = (bunsi % 10) * 5;
            }
            for (int i = 0; i < div5; i++)
            {
                bunsi = (bunsi % 10) * 2;
            }
            ans = bunsi % 10;
            
        }
        Console.WriteLine(ans);

    }

    private long GetKouyaku(long numA, long numB)
    {
        if (numA < numB)
        {
            return GetKouyaku(numB, numA);
        }
        long tmp = 0;
        do
        {
            tmp = numA % numB;
            numA = numB;
            numB = tmp;

        } while (tmp != 0);
        return numA;
    }


    public class Reader
    {
        public static bool IsDebug = true;
        private static String PlainInput = @"
 

95367431640626
95367431640625



 
";
        private static System.IO.StringReader Sr = null;
        public static string ReadLine()
        {
            if (IsDebug)
            {
                if (Sr == null)
                {
                    Sr = new System.IO.StringReader(PlainInput.Trim());
                }
                return Sr.ReadLine();
            }
            else
            {
                return Console.ReadLine();
            }
        }
        public static int[] GetInt(char delimiter = ' ', bool trim = false)
        {
            string inptStr = ReadLine();
            if (trim)
            {
                inptStr = inptStr.Trim();
            }
            string[] inpt = inptStr.Split(delimiter);
            int[] ret = new int[inpt.Length];
            for (int i = 0; i < inpt.Length; i++)
            {
                ret[i] = int.Parse(inpt[i]);
            }
            return ret;
        }
    }
    static void Main()
    {
        Program prg = new Program();
        prg.Proc();
    }
}