what was the total number of outputs of patient 7533 until 09/20/2105?
select sum(outputevents.value) from outputevents where outputevents.icustay_id in ( select icustays.icustay_id from icustays where icustays.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 7533 ) ) and strftime('%y-%m-%d',outputevents.charttime) <= '2105-09-20'