using System;

namespace _548
{
    class Program
    {
        static void Main(string[] args)
        {
            string s = Console.ReadLine();
            int[] a = new int[26];
            bool flag = true;
            for (int i = 0; i < s.Length; i++)
            {
                if (s[i] > 'm') flag = false;
                a[s[i] - 'a']++;
            }
            if (flag)
            {
                int two = 0; char ret = ' ';
                for (int j = 0; j <= 'm' - 'a'; j++)
                {
                    if (a[j] >= 2) two++;
                    else if (a[j] == 0) ret = (char)(j + 'a');
                }
                if (two > 1) Console.WriteLine("Impossible");
                else if (two == 1) Console.WriteLine(ret);
                else
                {
                    for (char i = 'a'; i <= 'm'; i++) Console.WriteLine(i);
                }
            }
            else Console.WriteLine("Impossible");
        }
    }
}