How can I make the menu stick after passing through a block?

Question

css

I made a vertical menu, when scrolling down, the text stands behind the footer, since there is a lot of it. I want it to reach the last block in front of the footer and stick, like this is implemented here. sticky01.blogspot.com/2013/09/5.html
Here is my creation, you can see all the code. Or I already have a menu done that will not help) How to make the menu text not go beyond the footer. Z index on top footer is not interesting. Who has any ideas)

Answer 1

It seems there is something similar, there when scrolling the block disappears (using js)
gnatkovsky.com.ua/fiksirovannyj-plavayushhij-blok-...