Need to find every nth value in a part of a column

Is there a way to retrieve every nth value in a part of a column?

My data looks like this:

A____________B_________C________D_______E______F
___________week1_____week2____week3___week4_____

January____13500______15000_____9000
February_______________8500_____7800
March__________________________4900____84000__5000
April____________________________5040____5400___4000
May
June


Now I know the formulas to select the first or the last entry within a column, in my case that would be:

First: =INDEX(S29:S45,MATCH(TRUE,INDEX(S29:S45<>0,0,0),0)) for week 2 gives me 15000 etc.
Last: =VLOOKUP(9.99999999999999E+307,S29:S45,1) for week 2 gives me 8500

What I now need is a formula that retrieves every second (and every third) entry within each column range. For week 3 for instance I need to get the 7800. Then in another step I need the 4900 etc.

Is there a way Excel retrieves every 2nd (and 3rd) value in a range (e.g. D5:D10)??