using System;
using System.Linq;

namespace No548
{
    public class Program
    {
        public static void Main(string[] args)
        {
            const string Tiles = "abcdefghijklm";
            var S = new string(Console.ReadLine().OrderBy(c => c).ToArray());

            if (S.Any(s => !Tiles.Contains(s)) || S.Distinct().Count() <= 11)
            {
                Console.WriteLine("Impossible");
                return;
            }

            if (S == Tiles)
            {
                Console.WriteLine(string.Join("\n", Tiles.ToCharArray()));
                return;
            }

            Console.WriteLine(Tiles.Except(S).Single());
        }
    }
}