instruction: get me the number of patients taking base drug type who have procedure icd9 code 3799.
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN procedures ON demographic.hadm_id = procedures.hadm_id INNER JOIN prescriptions ON demographic.hadm_id = prescriptions.hadm_id WHERE procedures.icd9_code = "3799" AND prescriptions.drug_type = "BASE"