how much is the difference between the total output and the total input of patient 3929 on this month/24?
select ( select sum(inputevents_cv.amount) from inputevents_cv where inputevents_cv.icustay_id in ( select icustays.icustay_id from icustays where icustays.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 3929 ) ) and datetime(inputevents_cv.charttime,'start of month') = datetime(current_time,'start of month','-0 month') and strftime('%d',inputevents_cv.charttime) = '24' ) - ( 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 = 3929 ) ) and datetime(outputevents.charttime,'start of month') = datetime(current_time,'start of month','-0 month') and strftime('%d',outputevents.charttime) = '24' )