(defun main (&rest argv)
  (declare (ignorable argv))
  (let* ((n (read))
         (dp (make-array (+ n 1) :initial-element 0)))
    (setf (aref dp 0) 1)
    (dotimes (i n)
      (incf (aref dp (+ i 1)) (aref dp i))
      (when (<= (+ i 2) n)
        (incf (aref dp (+ i 2)) (aref dp i))))
    (format t "~d~%" (aref dp n))))

(main)