using System;

namespace yukicoder
{
    class Program
    {
        static void Main(string[] args)
        {
              string a= Console.ReadLine();
            int b = a.Length;
            string str = "";
            string str1 = "";

            if (b%2==0)
            {
                str = a.Substring(0, b / 2);
                str1 = a.Substring(b / 2, b / 2);
                bool f = str.Equals(str1);
                if (f == true)
                {
                    Console.WriteLine("YES");
                }
                else
                {
                    Console.WriteLine("NO");
                }
            }
            else
            {
                Console.WriteLine("NO");
            }
            
        }
    }
}