Dimwit MDX count problem

I have run into a small problem. I have a dimension that identifies certain types of bills. I also have a measure that reports how many bills have been issued. There are several types of bills. But 1 of these is an adjustment bill. This is like a correction to an existing bill. These are represented as "A" bills in the DB

I need to count the number of unique bills, so that's a count of all the bills other than "A" bills.

I've looked at calculated members but am struggling with MDX syntax.

Anyone have any pointers or good articles I should read?

It should be something like this:`

with member [Measures].[Num]

as 'sum(except([Bills].[Level Name].members, [Bills].[ A ]), [Measures].[NumBills])'

Hope this helps,

Santi