[MS]Fill the rectangle with squares

Given a rectangle with known width and height, design an algorithm to fill the rectangle using n squares(n is integer given) and make sure in the result the wasting area is minimized. Length of square doesn't have to be integer.
i.e, given width=3,height=2,n=5, one solution is that rectangle can be filled with five 1x1 squares and the wasting area is 1. Another solution could be filled with five 0.9x0.9 squares, but the wasting area is more than first solution.