23 cubes
My answer is assuming the question uses the squares as units.
There are 20 whole squares
Two half squares= 1 square
There are 2 sets of 2 square spaces split from one corner to the opposite. They look to be split the same way, and to also be opposite halves of each other, like the two half squares mentioned before. However, this equals two squares, because 4 in total are split equally.
