c LEMON max flow problem
p max 7 9
n 1 s
n 7 t
a 1 2 3
a 1 3 2
a 1 4 1
a 2 5 3
a 3 5 2
a 3 7 5
a 3 6 3
a 4 6 1
a 5 7 2
a 6 7 4