+-------+  +-------+--+-------+  +------+
     |       |  |  +-+  |  |       |  |      ++
     |  +----+  |  | |  |  |  +----+  |  +-+  |
     |  |       |  | |  |  |  |       |  | |  |
     |  +--+    |  +-+ ++  |  +--+    |  | |  |
S----+     |    |   +--+   |     |    |  | |  +--->B
     |  +--+    |  +-+ ++  |  +--+    |  | |  |
     |  |       |  | |  |  |  |       |  | |  |
     |  |       |  | |  |  |  +----+  |  +-+  |
     |  |       |  | |  |  |       |  |      ++
     +--+-------+--+ +--+  +-------+--+------+