24b 
 +-----------------+
8| r r   r c   r   |
7| h     m r   d   |
6|     X r   X r R |
5| d c   e     h   |
4| r     E       R |
3|     X R C X H D |
2| H D C M R       |
1| R R R   R       |
 +-----------------+
   a b c d e f g h
