what was the total output for patient 14671 on this month/31?
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 = 14671 ) ) and datetime(outputevents.charttime,'start of month') = datetime(current_time,'start of month','-0 month') and strftime('%d',outputevents.charttime) = '31'