using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        var s = Console.ReadLine();
        var set1 = new HashSet<char>(s);
        var list1 =
            from c in "abcdefghijklm"
            select c;
        string ans = "";
        
        switch (set1.Count)
        {
            case 12:
                ans =
                    (from c in list1
                     where !set1.Contains(c)
                     select c).First().ToString();
                break;
            case 13:
                ans = string.Join("\n", list1);
                break;
            default:
                ans = "Impossible";
                break;
        }

        Console.WriteLine(ans);
    }
}