what was the length of stay of patient 72107 during 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 = 72107 ) and icustays.outtime is not null order by icustays.intime asc limit 1