###HUMAN: provide the number of patients whose procedure icd9 code is 5771 and drug type is main?, ###ASSISTANT: 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 = "5771" AND prescriptions.drug_type = "MAIN"