10
undirected
unweighted
a b c d e 1 2 3 4 5
a 1
b 2
c 3
d 4
e 5
a b
b c
c d
d e
e a
1 3
3 5
5 2
2 4
4 1
# petersen graph, see https://en.wikipedia.org/wiki/Petersen_graph
# the labeling used is abcde on the outside, with a at the top and going clockwise,
#  and 12345 on the inside, with 1 at the top going clockwise