Speed, speed function. And so if we wanted to actually integrate it, so if we wanted to integrate it, well, we don't know how to do it if we don't know, we don't know how to do it exactly without knowing the exact function. But we can approximate what the integral is going to be with a right Riemann sum. And a Riemann sum is just breaking up this area into rectangles and then finding the total area of those rectangles. And then there's a couple of ways you could do it. You could use, for each rectangle, you could use the left boundary as the height, or you could use the right boundary as the height. And so they tell us to use a right Riemann sum.