Find the volume of the region bounded by the paraboloid z = x^2 + y^2 + 4 and the planes x = 0, y = 0, z = 0, x + y = 1

So I believe that the limits are:

z : 0 to x^2 + y^2 + 4

y : 0 to 1-x

x : 0 to.... here's where I'm lost, if I set x = 1-y I wouldn't be able to solve this integral, right?

Also I don't understand what I'm supposed to be integrating, is it just x^2 + y^2 - z + 4 because it asks for the volume of the paraboloid?