Currently there are no reports available that report on the actual number of staff, due to reporting taking into consideration all employments on each person's profile.
However, you can run the Full Employee Data Extract and then filter the report in Microsoft Excel to remove duplicates.
Go to Reports and click Standard Reports.
Click Data Extract, then Full Employee Data Extract Report.
Select the parameters as needed and click Generate Extract.
Open the report in Microsoft Excel.
Column A, EmployeeNumber, will display the employee number for each employment.
Column B, PrimaryEmploymentNumber, will display the primary employment of the person. This column will contain duplicates if the employee has more than one employment.