calculate the length of patient 28484's stay at the first intensive care unit stay.
select strftime('%j',icustays.outtime) - strftime('%j',icustays.intime) from icustays where icustays.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 28484 ) and icustays.outtime is not null order by icustays.intime asc limit 1