(defun fish (a b)
  (let* ((veca (coerce a 'vector))
         (vecb (coerce b 'vector))
         (size (length veca))
         (dead 0)
         (stack '()))
    (dotimes (i size)
      (if (= (aref vecb i) 1)
          (push (aref veca i) stack)
          (when stack
            (loop while stack
                  do (progn
                       (incf dead)
                       (if (> (aref veca i) (first stack))
                           (pop stack)
                           (return)))))))
    (- size dead)))