Show Row Totals conditionally in a matrix

I have a Matrix with a column group on a field called FAC for Facility.  The rows are a field called DRGGroup and the calculated field in the Matrix is

=Count(Fields!PAT_ACCT_NBR.Value)

I have a parameter set up called Facility with three possible values:  A, C, and F. 

I want to add a totals column at the end which will sum the three Facility by DRGGroup but I only want to show this total if the user selects all three Facilities.  If they only select one or two facilities I want to supress the totals column from showing.  I am familiar with the Column Visibility option and know I can write an expression but can't get the syntax down. 

Thanks,

Chuck

Chuck W