(defun main (&rest argv)
  (declare (ignorable argv))
  (let* ((s (read-line))
         (n (length s))
         (n/2 (floor (length s) 2)))
    (format t "~A~%" (if (string= (subseq s 0 n/2)
                                  (subseq s n/2 n))
                                  "YES"
                                  "NO"))))

(main)