A        
 2       
         
A        
 /1\     
 |-|     
 \2/     
      _  
    \/2  
         
/A   \   
| /1\|   
| |-||   
\ \2//   
        _
      \/2
         
A        
 //1\   \
 ||-|   |
 |\2/   |
 |     _|
 \   \/2/
         
       1 
A    + - 
 421   2 
         
A        
 421     
----     
  2