Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE management (department_id VARCHAR); CREATE TABLE department (department_id VARCHAR)
### Question:
How many departments are led by heads who are not mentioned?
### Answer:
SELECT COUNT(*) FROM department WHERE NOT department_id IN (SELECT department_id FROM management)