15
   
                      
   
      ------------------------------------------------------------------
      |                   |     |
      ---------------------------------------------             |
      ||                        |                    |
      ----------------------------------------------------------------
      |      |                                    |   --------------   |
      |  1   |                                |   |     |   |
      |      |                                    |   --------------   |
      ----------------------------------------------------------------
      |      |                                    |   --------------   |
      |  2   |                                 |   |     |   |
      |      |                                    |   --------------   |
      ----------------------------------------------------------------
      |      |                                    |   --------------   |
      |  3   |                              |   |       |   |
      |      |                                    |   --------------   |
      ----------------------------------------------------------------
      |  4   |                         |   --------------   |
      |  5   |                       |   |      |   |
      |      |                                    |   --------------   |
      ----------------------------------------------------------------
      |      |                                    |   --------------   |
      |  6   |                             |   |   |   |
      |      |                                    |   --------------   |
      ----------------------------------------------------------------
      |      |                                    |   --------------   |
      |  7   |                              |   |  |   |
      |      |                                    |   --------------   |
      ----------------------------------------------------------------
      |  8   |                     |   --------------   |
      |  9   |                   |   |  |   |
      |      |                                    |   --------------   |
      ----------------------------------------------------------------
      |      |                                    |   --------------   |
      |  0   |                      |   |       |   |
      |      |                                    |   --------------   |
      ----------------------------------------------------------------