All of it.
Joking aside, I think the maths is only necessary if you want to have an easier time training, testing, and debugging, but you could probably get by and still learn a lot without an intense maths background. At the very least you'll learn the concepts and might pick up some math knowledge along the way.
There's a neat Youtube channel I recommend checking out called "Siraj Raval" (creator's name I assume). He does a lot of quick machine learning examples at a fast pace, so there's not much fluff to get bored with.