Excel formula - If function (maybe?)

I'm looking for the cell directly below the most recent data input to show the difference in values for the two cells above.

Column A has dates, columns B & C have Gain/loss in USD and % respectively, D: market value, E: total cost, as depicted below (value are obviously simply for representation)

So potential formula for B4 would include the following arguments
- If A3 has a value and A4 is blank then calculate formula '=B3-B2'
- If both A3 & A4 have values then calculate formula '=D4-E4'
- If both A3 & A4 are blank leave cell value at '-'

	A	B	C	D	E
1	Date	Gain/Loss ($)	Gain/Loss (%)	Value	Cost
2	9/08	$10	3%	$20	$10
3	9/09	$12	3.5%	$22	$10
4	Blank	$2.0	0.5%	-	-
5	Blank	-	-	-	-

Currently I am using '=IF(OR(A#=""),"-",(D#-E#))' to calculate USD and % gain/loss if there's a date value present in column A and to leave as '-' if blank.