Want a cell to change which cell it references based on content in adjacent cells

I am making a sales ledger for a little fun and am wanting to track month to date and year to date sales in a single cell.
I am attempting to make cell C36 to reference whichever cell in column C has most recently filled in. This means that at the end of each night, when we input the sales total for the day, cell C36 will change. I see one of two ways to do this:
1) Make cell C36 reference the corresponding total in column D OR
2) Make cell C36 reference the sum of the days up to that point.

I would prefer option 2 but I am willing to go with whatever at this point.
See attached photos for how the cells will change day-to-day

Day 1
Grab 1.jpeg

Day 2
Grab 2.jpeg

Day 3
Grab 3.jpeg