Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE CLASS (PROF_NUM VARCHAR)
TABLE: CREATE TABLE employee (EMP_NUM VARCHAR, EMP_LNAME VARCHAR)

### Question ###
How many classes are professor whose last name is Graztevski has?

### Accurate SQL ###

SELECT COUNT(*) FROM employee AS T1 JOIN CLASS AS T2 ON T1.EMP_NUM = T2.PROF_NUM WHERE T1.EMP_LNAME = 'Graztevski'