using System;
using static System.Console;
using static System.Math;

public class Hello{
    public static void Main(){
//        int kazu = int.Parse(ReadLine());
//        string[] temp = ReadLine().Split(' ');
//        int a = int.Parse(temp[0]);
//        int b = int.Parse(temp[1]);

        string word = ReadLine();
        int wl = word.Length;
        string x = word.Substring(0,wl/2);
        string y = word.Substring(wl/2);
        if(x == y){
            WriteLine("YES");
        }else{
            WriteLine("NO");
        }
    }
}