total flow: 4
flow values:
flow(0,1) = 4
flow(1,2) = 4
flow(2,3) = 2
flow(2,4) = 2
flow(3,1) = 0
flow(3,6) = 2
flow(4,5) = 3
flow(5,6) = 0
flow(5,7) = 3
flow(6,4) = 1
flow(6,7) = 1