class Program
{
    static void Main(string[] args)
    {
        string input = Console.ReadLine()!;

        string left = input.Remove(input.Length / 2, input.Length / 2);
        string right = input.Remove(0, left.Length);

        if (left == right)
        {
            Console.WriteLine("YES");
        }
        else
        {
            Console.WriteLine("NO");
        }
    }
}