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

public class Program
{

    public void Proc()
    {
        string target = "abcdefghijklm";
        string input = Reader.ReadLine();
        bool isPossible = true;
        if(input.Any(a=>!target.Contains(a))) {
            isPossible = false;
        }
        if(isPossible) {
            if(input.Any(a=>input.Count(b=>b==a)>2)) {
                isPossible = false;
            }
        }
        if(isPossible) {
            if(input.All(a=>input.Count(b=>b==a)==1)) {
                target.OrderBy(a => a).ToList().ForEach(a=>Console.WriteLine(a));
            } else {
                Console.WriteLine(target.First(a=>!input.Contains(a)));
            }
        } 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 = @"


cbmlieadfghjk

";
	}

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