How many Space Marines would it take to beat the Gungan army in Episode I? (Star Wars/WH40k)

Some disgusting underwater Xenos that have been hiding out on a human planet are marching to war. The Imperium is happy to take the opportunity to slaughter their army. A Space Marine Chapter is around and volunteers to go take care of the issue. How many Battle Brothers would they have to send to destroy the army from The Phantom Menace and kill all of the Gungans?

The Astartes can be from any era or gene line. 40k Ultramarines, 30k Night Lords, whatever. Everyone is a basic Space Marine, so no Terminators, Dreadnaughts, etc. No Librarians, sorcerers, Wolf Priests, or any other type of psykers are available either. The Gungan Army is as it was in the movie. The Space Marines attack from the position of the droid army.

• Round 1: How many Space Marines does it take to bring down the Gungan Grand Army?

• Round 2: The Space Marines replace the Gungans instead. How many does it take to bring down the droid army? There are no space assets, so the control ship won't be destroyed.