instruction: what is patient 13473's last ward id until 4 years ago?
response: SELECT transfers.wardid FROM transfers WHERE transfers.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 13473) AND NOT transfers.wardid IS NULL AND DATETIME(transfers.intime) <= DATETIME(CURRENT_TIME(), '-4 year') ORDER BY transfers.intime DESC LIMIT 1