using System;

namespace _6._MiddleCharacters
{
    class MiddleCharacters
    {
        static void Main()
        {
            string word = Console.ReadLine();

            Console.WriteLine(GetMiddleCharacter(word));
        }

        static string GetMiddleCharacter(string word)
        {
            string middleChar = null;

            if (word.Length % 2 == 1)
            {
                middleChar = word[word.Length / 2].ToString();
            }

            else
            {
                middleChar = word[word.Length / 2 - 1].ToString() + word[word.Length / 2].ToString();
            }


            return middleChar;
        }
    }
}