Trade Nations

There are $N$ nations in ByteLand. Every nation wants to do trade with the other nations. In order to enable this trade, the nations start signing trade treaties. The $i_{th}$ trade treaty is an agreement between two nations $x_i$ and $y_i$ for trading goods at a fixed price $c_i$. Countries which have trade treaties signed between them can also deliver goods to each other (which they might've bou