instruction: provide the number of patients who have the admission location as transfer from hosp/extram and diagnosis icd9 code as 4820.
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id WHERE demographic.admission_location = "TRANSFER FROM HOSP/EXTRAM" AND diagnoses.icd9_code = "4820"