using System;

    class Program {
        static void Main(string[] args) {
            string answer = null;

            string read = Console.ReadLine();
            char[] cs = read.ToCharArray();
            Array.Sort(cs);

            if (new string(cs) == "abcdefghijklm") {
                answer = @"a
b
c
d
e
f
g
h
i
j
k
l
m";
            } else {

                for (char c = 'a'; c < 'n'; c++) {
                    int cnt = 13 - read.Replace(c.ToString(), "").Length;
                    if (cnt == 0) {
                        if (answer == null) {
                            answer = c.ToString();
                        } else {
                            answer = "Impossible";
                            break;
                        }
                    }
                }
            }
            Console.WriteLine(answer);
            Console.Read();

        }
    }