using System;
using System.Linq;

namespace No739
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var S = Console.ReadLine();

            if (S.Length % 2 == 1)
            {
                Console.WriteLine("NO");
                return;
            }

            var ans = S.Take(S.Length / 2).SequenceEqual(S.Skip(S.Length / 2));
            Console.WriteLine(ans ? "YES" : "NO");
        }
    }
}