calculate the length of the hospital stay of patient 16248's first icu 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 = 16248 ) and icustays.outtime is not null order by icustays.intime asc limit 1