<image> (2013•Zhenhai District School-Level Independent Recruitment) There are a number of small cubes of the same size piled up in the corner to form the three-dimensional shape as shown in the image. If you plan to move some of the small cubes (without considering the limitations of operation technique), but want the shadows on the walls and floor to remain the same when illuminated with parallel rays from the front, from the top, and from the right side, then the maximum number of small cubes you can move is_____.