.
                                       o
                             w    w  n     w
                          n        o   w        n
                        o             n               o
                       w             o                w
                      n              w                 n
                     o                n                  o
                     w           o      w             w
                     n            n       o             n
                      o             w   n             o
                       w             o                w
                         n            w             n
                            o          n          o
                               w      o       w
                                   n   w   n
                                         n