Well, I'm trapped in a level of the first episode. In this puzzle:

I've placed the IV and IX numbers in their respective marked squares, and two doors opened. But the third one remains closed. Then I ordered all the numbers -"solving" the puzzle, one could say-, but nothing happens. What to do in order to open the third door?
Maybe somebody here had also played this game and solved that level...
Thanks, and sorry for my broken english.