BoxUp Puzzle

This is a puzzle similar to traditional Sokoban.
But here all the boxes are hollow and open on one side.
They can only be moved by pushing from the inside.
There are two sizes of boxes, small and large.
The aim is always to push the small red box inside the blue box.
Black boxes may help or hinder your progress.
A small box inside a large box can be pushed together.
BoxUp is a flash remake of an Andrea's Gilbert puzzle (clickmazes.com).
Programming by Nick Kouvaris © 2005.