So the area of each of these rectangles, the base is two, and the height is f of two n minus, f of two n minus one. So that's, that hopefully makes a little bit clearer, kind of mapping between the sigma notation and what we're actually trying to do. And now let's just, just for fun, let's actually try to evaluate this thing. What is this thing going to evaluate to? Well, this is going to evaluate to two times f of, when n is equal to one, this is one, f of one, plus two times, when n is two, this is going to be f of two times two minus one is three, f of three. When n is three, this is going to be two times f of five. When n is four, this is going to be two times, two times f of seven.