Tip 1:

Let us suppose that we give you a maximal flow as an input and you
want to minimize the cost. Can you solve this problem?




































































Tip 2:

The solution is just max_F( cost of flow with pipe of flow ≤ F / F)




























































Tip 3:
Apply solution of tip 1 for each possible maximal value of flow (1..1000) and use Tip 2.