using System;
using System.Linq;

public class Yuki548
{
	public static void Main()
	{
		var s = Console.ReadLine();
		var str = "abcdefghijklm";
		var x = s.Distinct().Count(c => str.Contains(c));
		if (x == 13) foreach (var c in str) Console.WriteLine(c);
		else if (x == 12)
		{
			var ch = str.First(c => !s.Contains(c));
			Console.WriteLine(ch);
		}
		else Console.WriteLine("Impossible");
	}
}