+-----+-----+-----+-----+-----+
|     |     |     |     |     |
|     x     x     x     x     |
|     |     |     |     |     |
+-----+--x--+-----+-----+-----+
|     |     |     |     |     |
|     x     |     x     x     |
|     |     |     |     |     |
+--x--+-----+--x--+-----+--x--+
|     |     |     |     |     |
|     x     x     x     |     |
|     |     |     |     |     |
+-----+--x--+-----+--x--+-----+
|     |     |     |     |     |
|     x     |     |     x     |
|     |     |     |     |     |
+--x--+-----+--x--+--x--+-----+
|     |     |     |     |     |
|  S  x     x     |     x     |
|     |     |     |     |     |
+-----+-----+-----+-----+-----+