using System;
using System.Linq;

namespace y
{
    class Program
    {
        static void Main(string[] args)
        {
            string s = Console.ReadLine();
            string ans = "";
            bool f = true;

            foreach (var c in s)
            {
                int a = s.Count(x => x == c);
                if (a > 2)
                {
                    f = false;
                    break;
                }
                if (a == 1)
                {
                    ans += c.ToString();
                }
            }

            if (!f || ans.Length >= 2) Console.WriteLine("Impossible");
            else Console.WriteLine(ans);
        }
    }
}