using System;

public class Hello
{
    public static void Main()
    {
        var s = Console.ReadLine().Trim();
        Console.WriteLine(check(s) ? "YES" : "NO");
    }
    public static bool check(string s)
    {
        var sL = s.Length;
        if (sL % 2 == 1) return false;
        var s1 = s.Substring(0, sL / 2);
        var s2 = s.Substring(sL / 2);
        return s1 == s2;
    }
}