1                                                                                                      2                                                                                                        3

                                        1                                                                                                           2                                                                                                       1                                                                                                 2

                                     4                                                                                                       1                                                                                                             2                                                                                                  3

                                 1                                                                                                            2

                                      4                                                                                                         5                                                                                                        6                                                                                                      7

                                           1                                                                                                      2                                                                                                       3