        10 
                                 
1       
                                                          
2         
                                                                                        
3           
                                                              
                                             
4        
                                                            
                
         
5       
                            
                    
                                      
6        
                                                                                         
7     
                                                                         
                                      
8       
                        
                 
                                               
9         
                                                        
                                                       
10          
                                                                      

    20 17   10  15    