using System;

class Program
{
    public void Solve()
    {
        string S = Console.ReadLine();
        Console.WriteLine(S.Substring(0, S.Length / 2) == S.Substring(S.Length / 2) ? "YES" : "NO");
    }

    static void Main()
    {
        var solver = new Program();
        solver.Solve();
    }
}