Need to Adjust Cost Basis on a Long Term Noncovered Security

My 1099-B lists the proceeds but not the cost basis for a long term noncovered security sale through Computershare.  I have documentation from Computershare at the time of the sale that shows the cost basis.  In this case the cost basis is more than the proceeds, so a net loss.

 

I've checked the box that says "I need to adjust my total cost basis" and below that it says "Total adjustments to gain (or loss)" with a box to enter a number.  That box won't allow me to enter a (loss), it won't accept parentheses and any amount I put in that box gets added to the total proceeds.  What am I supposed to report in this box and how do I do it?  I have checked adjustment code B (cost basis incorrect on form) for the reason for the adjustment.

 

Thanks in advance for any help.