1999 AIME Problem 6

A transformation of the first quadrant of the coordinate plane maps each point (x, y) to the point (\sqrt{x}, \sqrt{y}). The vertices of quadrilateral A B C D are A=(900,300), B=(1800,600), C=(600,1800), and D=(300,900). Let k be the area of the region enclosed by the image of quadrilateral A B C D. Find the greatest integer that does not exceed k.