[(0,1),(1,2),(0,2),(1,3),(2,4),(4,5),(5,6),(4,7),(7,8),(6,9),(5,10),(8,11),(9,12),(3,13),(7,14),(8,15),(6,16),(9,17),(10,18),(3,19),(10,20)]
[(0,1),(1,2),(1,3),(3,4),(0,4),(2,5),(2,6),(5,7),(4,8),(6,9),(9,10),(7,11),(10,12),(6,13),(7,14),(9,15),(8,16),(10,17),(5,18),(8,19),(3,20)]
