Stair builder 3

Got it

Congrats to be featured at official Mekorama FB page!

Spoiler: Last step.

I am in the center and R is free, but... Has R to be in the the upper floor or under the red dot?

Finally I did it! Very difficult, is the hardest of the three. It's surprising, when you think that you have the solution, another problem appears. Very good level. Thank you very much!

Wow!! As previous ones a very challenging puzzle!! I sweated blood to solve it!! But what satisfaction !! More trickier but at least a difficult logic level with one trick and one surprise!! Thanks for sharing and excellent job @vince