using System;

namespace yukicoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var line = Console.ReadLine();
            var len = line.Length / 2;
            var st1 = line.Substring(0, len);
            var st2 = line.Substring(len);
            
            string msg = (st1 == st2) ? "YES" : "NO";
            Console.WriteLine(msg);
        }
    }
}