(defun fib-frog (a)
  (let* ((vec (coerce a 'vector))
         (size (length vec))
         (fib (make-array 2 :initial-contents '(0 1) :adjustable t :fill-pointer 2)))
    (let ((i 1))
      (loop while (<= (aref fib i) size)
            do (progn
                 (incf i)
                 (vector-push-extend (+ (aref fib (1- i)) (aref fib (- i 2))) fib))))
    (let ((paths (list (list :idx -1 :jmp 0)))
          (steps (make-array size :initial-element nil)))
      (loop while paths
            do (let ((path (pop paths)))
                 (loop for i from (1- (length fib)) downto 2
                       do (let ((idx (+ (getf path :idx) (aref fib i))))
                            (cond
                              ((= idx size) (return-from fib-frog (1+ (getf path :jmp))))
                              ((or (> idx size)
                                   (aref steps idx)
                                   (zerop (aref vec idx)))
                               nil)
                              ((= (aref vec idx) 1)
                               (setf (aref steps idx) t)
                               (setf paths (append paths (list (list :idx idx :jmp (1+ (getf path :jmp))))))))))))
      -1)))