using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;
using static System.Console;
using static System.Math;

namespace CP
{
    class Atria
    {
        static void Main(string[] args)
        {
            string s = ReadLine();
            WriteLine(
                s.Substring(0, s.Length / 2) == s.Substring(s.Length / 2, s.Length/2)&&s.Length%2 == 0
                ? "YES":"NO"
                );
        }
    }
}