SUM Expression

Hello,

In my SSRS I have two values of Fields!Role.Value = "Contractor" and "Manager". What is the SSRS expression to SUM of how many contractor or manager on the report? For example, I want to sum of how many contractor we have and how many of manager we have when we run a report in SSRS?

SUM(IIF(Fields!Role.Value="Contractor",1,0))