Narrative Reporting Formula - Ignore negative values in sum

Hi, In narrative reporting I have a number of conditional suppressions in my report for negative values. I am trying to only sum the positive values for a certain range of rows and would like to ignore any negative values in my sum. I am using a custom formula and have the following formula:
[2]+[3]+[5]+[7]+[8]+[9]+[10]+[31]+[32]+[33]+[34]+[35]+[36]+[37]+[38]+[39]+[40]+[41]

If rows 31 - 40 are negative, I would like to ignore in my sum.

Thanks for your help in advance!