Originally Posted by Happy

For once, BonVoy is correct. It has said it Very Clearly on the 5th night free benefit, that the free night is on the lowest cost night, not on the 5th night in the sequence sense.
Also on the reservation, even before you finalize it - the Summary of Charge when clicked open, you will readily see WHICH night is the free night. It can be any night in the group of the 5, as long as that night is the lowest cost night.

In a rare case, say, there is an off peak, standard and peak, all in the same 5 nights - you would be charged 145K because only the 30K is free, leaving 35K x 3 + 40K x 1 = 145K.

The 5th night free takes the lowest cost night being free, not by sequence. Therefore the 30K night is your free night, leaving you 4 x 35K nights. I think someone before me has already pointed it out though you may just look at the total without looking at the daily rate of each night.