using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static long NN => long.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var s = ReadLine();
        var count = new int[26];
        foreach (var c in s) ++count[c - 'a'];
        if (count.Count(ci => ci == 1) == 1 && count.Count(ci => ci == 2) == 6)
        {
            for (var i = 0; i < 26; ++i) if (count[i] == 1) WriteLine($"{(char)(i + 'a')}");
        }
        else WriteLine("Impossible");
    }
}