using System;
using System.IO;
using System.Linq;
using System.Collections.Generic;
using System.Text;

public class Program
{

    public void Proc()
    {
        string inpt = Reader.ReadLine();
        Dictionary<char, int> cnt = new Dictionary<char, int>();
        inpt.ToList().ForEach(a=>{
            if(cnt.ContainsKey(a)) {
                cnt[a]++;
            } else {
                cnt[a] = 1;
            }
        });

        if(cnt.Count == 7 && cnt.Count(a=>a.Value == 2) == 6 && cnt.Count(a=>a.Value == 1) == 1) {
            Console.WriteLine(cnt.Where(a => a.Value == 1).First().Key);
        } else {
            Console.WriteLine("Impossible");
        }
    }





    public class Reader
    {
        private static StringReader sr;
        public static bool IsDebug = false;
        public static string ReadLine()
        {
            if (IsDebug)
            {
                if (sr == null)
                {
                    sr = new StringReader(InputText.Trim());
                }
                return sr.ReadLine();
            }
            else
            {
                return Console.ReadLine();
            }
        }
        private static string InputText = @"


hsgeeappashoo



";
    }

    public static void Main(string[] args)
    {
#if DEBUG
        Reader.IsDebug = true;
#endif
        Program prg = new Program();
        prg.Proc();
    }
}