using System;

class Program
{
    static void Main()
    {
        var s = Console.ReadLine();
        var len = s.Length;
        if (len % 2 == 0)
        {
            var L = s.Substring(0, len / 2);
            var r = s.Substring(len / 2);
            if (L == r)
            {
                Console.WriteLine("YES");
                return;
            }
        }
        Console.WriteLine("NO");
    }
}