(defun stone-blocks (h)
  (let* ((n (length h))
         (height (make-array n :initial-element 0))
         (index 0)
         (blocks 0))
    (dolist (i h)
      (loop while (and (> index 0) (> (aref height (1- index)) i))
            do (decf index))
      (unless (and (> index 0) (= (aref height (1- index)) i))
        (setf (aref height index) i)
        (incf blocks)
        (incf index)))
    blocks))