how many times in 05/last year did patient 1903 produce a tf residual output?
select count(*) 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 = 1903 ) ) and outputevents.itemid in ( select d_items.itemid from d_items where d_items.label = 'tf residual' and d_items.linksto = 'outputevents' ) and datetime(outputevents.charttime,'start of year') = datetime(current_time,'start of year','-1 year') and strftime('%m',outputevents.charttime) = '05'