Here is the question...

Fine exactly the volume under the surface $\displaystyle z=(1-x^2)(1-y^2)$ in the first octant.

Can someone solve this and explain to me how to do it? The main thing I am confused about is how to find the limits. I know I am supposed to use the fact that it is in the first octant to find the limits, but I am not sure what to do with that information. Thanks in advance.