Selling Metal For Deuterium

I'm offering equal amounts of Metal for anyone looking to get rid of Deuterium.

I'll offer 10,000 for 10,000

I'll offer 100,000 for 100,000

For every 5,000 Deuterium you trade me though, I'll throw in an extra 1,000 Metal

So if you trade me 4,000 you get 4,000

But if you trade me 8,000 you get 9,000

Trade me 10,000 you get 12,000

Cheers.