14 First lesson in a new class

   1      2        3   4      5        
            6       7         
  8     9                     
               10           
 11           12                
13           14                 
15       16        17               
    18                19        
           20     21          22    
    23                      
              24    25          
   26     27        28          29      
 30            31         32        
33        34      35          36        
               37           
   38                  39       
40                41