(defun main (&rest argv)
  (declare (ignorable argv))
  (let* ((n (read))
         (a (make-array 36 :element-type 'integer :initial-element 0))
         (res 0))
    (loop for i from 1 to n do
          (incf (aref a (read))))
    (loop for i from 1 to 35
          when (zerop (aref a (1- i)))
            do (incf res (* i (aref a i))))
    (format t "~d~%" res)))

(main)