.

                                    B
                           o      o w       o
                        w        s  B         w
                       s           ow            s
                      B             s              B
                      o             B              o
                      w         o    w         w
                        s         s     B         s
                         B        o  w        B
                           o       B  o       o
                               w    w     w
                                       S