Detecting last cell within a block

[Funk]

I know some basic VBA, but not enough to do what I want.
So far, all I could figure out was how to find the last cell on a row within a range of rows. But I don't know yet how to perform a loop detecting the first and last rows of every block, and to use that to find the last cell for each.
I thought there must be a way for a pro to do that within a few lines of code. But if it is going to get too complicated, then maybe I should just forget about it.

(Changing the distribution of the input data is not a possibility)