using System;

namespace StudyApp
{
    class Program
    {
        static void Main(string[] args)
        {
            string s = Console.ReadLine().Trim();
            int length;

            if ((length = s.Length % 2) == 0)
            {
                string firstWord = s.Substring(0, length);
                string secondWord = s.Substring(length, length);

                if (firstWord.Equals(secondWord))
                    Console.WriteLine("YES");
                else
                    Console.WriteLine("NO");
            }
            else
            {
                Console.WriteLine("NO");
            }
        }
    }
}