So it's going to have some depth, dx. So this is my best attempt at drawing some of that to depth. So this is the depth of our washer. And then just to make the face of the washer a little bit clearer, let me do it in this green color. So the face of the washer is going to be all of this business. So if we can figure out the volume of one of these washers for a given x, then we just have to sum up all of the washers for all of the x's in our interval. So let's see if we can set up the integral.