This was kind of our end of our interval. This is until x is equal to... Let me be careful. This is the x-axis right over here. This is the x-axis right over here, all the way until x equals 4. You get confused. This is the x-axis. We're going from x equals 1 to x equals 4, and we're essentially taking this area, one way to think about it, between our square root of x and 1, and we're rotating it around 1.