c This is a sample shortest path problem
c
p sp 6 8
c 6 nodes 8 arcs
c
a 1 2 1
c arc from node 1 to node 2 of length 1
c
a 1 3 10
a 2 4 2
a 3 5 0
a 4 3 0
a 4 6 3
a 5 2 0
a 5 6 20
