.
                                   O
                           r     r  c      r
                        c        h  i         c
                      h           d             h
                    i              O               i
                   d              r                 d
                   O          c      h            O
                   r           i       d             r
                    c           O    r             c
                     h             c               h
                      i             h              i
                        d           i            d
                          O        d         O
                              r     O    r
                                     r
                                     c
                                     h
                                     i
                                     d