(defun main (&rest argv)
  (declare (ignorable argv))
  (let* ((kr (read))
         (kb (read))
         (s1 (read-line))
         (cs (make-array 31 :element-type 'integer))
         (tmp 0)
         (ma 0))
    (dotimes (i 30)
      (if (char= #\W (aref s1 i))
          (setf (aref cs i) 21)
          (setf (aref cs i) tmp
                tmp (1+ tmp))))
    (dotimes (i 1048576)
      (let ((s2 "")
            (ok 1))
        (dotimes (j 30)
          (when (zerop (logand i (ash 1 (aref cs j))))
                (setf s2 (concatenate 'string s2 (string (aref s1 j))))
                (when (and (char= #\R (aref s1 j))
                           (> (length s2) kr)
                           (char= #\R (aref s2 (- (length s2) kr 1))))
                      (setq ok 0))
                (when (and (char= #\B (aref s1 j))
                           (> (length s2) kb)
                           (char= #\B (aref s2 (- (length s2) kb 1))))
                      (setq ok 0))))
        (unless (zerop ok)
          (setq ma (max ma (length s2))))))
    (format t "~d~%" ma)))

(main)