tell me the last careunit patient 28020 got during their first hospital visit?
select transfers.careunit from transfers where transfers.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 28020 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and transfers.careunit is not null order by transfers.intime desc limit 1