Find Average Of Last 4 Non Zero Numbers

I am trying to figure out how to take the average of the last 4 "non-zero" numbers in a series of values.

The sheet looks something like this, numbers are all in one row:

7 , 7 , 7 , 7 , Total = 28 , 8 , 8 , 8 , 8 , Total = 32 , 0 , 0 , 0 , 0 , Total = 0 , 8 , 8 , 8 , 8 , Total = 32 , 7 , 7 , 7 , 7 , Total = 28 , 8 , 8 , 8 , 8 , Total = 32 , 0 , 0 , 0 , 0 , Total = 0 , 8 , 8 , 8 , 8 , Total = 32

I'm looking for a formula that will look at all the last few totals (starting from the end) and take an average of the last 4 totals that were > 0. In this case it would average {32, 32, 28, 32} ignoring the 0 total.