I am trying to sum all numbers <0 using the SUMIF formula in Excel 2003.

FORMULA: =sumif(range,criteria,sum_range)

I got it to work, but I have cell ranges to total that are not next to each
other (such as A5:A15 and C5:C15).
When selecting the ranges for the formula, Excel writes them A5:A15,C5:C15

because of the comma (,) between the cell ranges Excel is reading the A5:A15
as the range and C5:C15 as the critera. How can I get this formula to allow
me to select multiple cell ranges?

All help is appreciated.

Thank you.