but from the 5 chocolate wrappers you exchange for one more, so you are left with 2 wrappers, but since you bought another chocolate, now you have 3 wrappers again, so you can have one more chocolate, so it's 22
it's actually quite easy to overlook the fact that after you exchange the 5 wrappers for one more chocolate, you get one extra wrapper to add with the other 2 left
