Counting Total Rows When Using GROUP BY

hi,

i have a stored procedure SELECT UserName AS Visitor, COUNT(VisitID) AS TotalVisit
FROM UserVisits
WHERE (ProductID = @ProductID) AND (AnonimIP IS NULL)
GROUP BY UserName
UNION
SELECT AnonimIP AS Visitor, COUNT(VisitID) AS TotalVisit
FROM UserVisits AS UserVisits_1
WHERE (ProductID = @ProductID) AND (UserName IS NULL)
GROUP BY AnonimIP

this will return something like:

zuperboy90 - 4 visits

ANONIMOUS - 6 visits

85.104.103 - 2 visits etc

how can i count the rows returned in both selections (4+6+2 = 12) ?

thank you