|  * *                          
            |    *       *                  
            |      *   *                    
            |        * *                    
          5 -          * *                  
            |            *                 *
            |              *   *            
            |                * *            
            |                  *       *    
         10 -                    *   *      
            |                      * *      
            |                        * *    
            |                          *   *
            |                            * *
         15 -                              *
            |----------|---------|---------|
                       5        10        15