using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace yukicoderTest
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = Console.ReadLine();
            if(input.Length%2==1)
            {
                Console.WriteLine("NO");
            }
            else
            {
                string temp = input.Substring(0, input.Length / 2);
                input = input.Remove(0, input.Length / 2);
                if(temp==input)
                {
                    Console.WriteLine("YES");
                }
                else
                {
                    Console.WriteLine("NO");
                }
            }

        }
    }
}