(defun sleep-to-awake-transitions ()
  (let ((n (read))
        (s (read-line))
        (result '()))
    (loop for k from 2 to n
          when (and (char= (aref s (- k 2)) #\x)
                    (char= (aref s (- k 1)) #\o))
          do (push k result))
    (setq result (nreverse result))
    (format t "~d~%" (length result))
    (format t "~{~a~^ ~}~%" result)))

(sleep-to-awake-transitions)