Writing a query to COUNT all the services involving a particular Learning PHP and SQL on an online MOOC, this is a homework that I've got to do.

I need to write a query in SQL to count all the services which involve a particular person in my database. 

The particular's name is Gary Crowley located in the 'staff' table. 
Below is my table:
 

My question is: What is the actual SQL query I should write to get the exact count of all the services which involve Gary Crowley? As you can see in the picture, the name appears four times. I have written a query that output the services only involving Gary Crowley but I don't know how to make the COUNT query.
select count(distinct service_id)
from staff
where staff_firstname = 'Gary'
  and staff_surname = 'Crowley';


The distinct is only necessary if your database design allows to assign the same service multiple times to the same staff member.