instruction: count the number of patients with drug code keto15i who were admitted in hospital via clinic referral/premature.
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN prescriptions ON demographic.hadm_id = prescriptions.hadm_id WHERE demographic.admission_location = "CLINIC REFERRAL/PREMATURE" AND prescriptions.formulary_drug_cd = "KETO15I"