(defun main (&rest argv)
  (declare (ignorable argv))
  (let* ((n (read))
         (m 0))
    (loop for i from 1 to n do
          (let ((l (+ i (* (- n i) (1+ i)))))
              (when (> l m)
                    (setq m l)))
          finally (format t "~D~%" m))))

(main)