using System;
using System.Linq;

namespace y
{
    class Program
    {
        static void Main(string[] args)
        {
            char[] cs = Console.ReadLine().ToCharArray().Distinct().ToArray();

            if (cs.Count(x => x > 'm') >= 1)
            {
                Console.WriteLine("Impossible");
                return;
            }

            if (cs.Length == 12)
            {
                for (int i = 0; i < 13; i++)
                {
                    if (cs.Count(x => x == ('a' + i)) == 0) Console.WriteLine((char)('a' + i));
                }
            }
            else if (cs.Length == 13)
            {
                for (int i = 0; i < 13; i++)
                {
                    if (cs.Count(x => x == ('a' + i)) == 1) Console.WriteLine((char)('a' + i));
                }
            }
            else
            {
                Console.WriteLine("Impossible");
            }
        }
    }
}