c nb_vertices=13 nb_token=2
c LENGTH 11
a YES
a 1 8 
a 2 8 
a 2 9 
a 3 9 
a 3 10 
a 4 10 
a 4 11 
a 5 11 
a 5 12 
a 6 12 
a 6 13 
a 7 13