how many times did patient 31854 in 12/2105 receive br milk fs po?
select count(*) 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 = 31854 ) ) and inputevents_cv.itemid in ( select d_items.itemid from d_items where d_items.label = 'br milk fs po' and d_items.linksto = 'inputevents_cv' ) and strftime('%y-%m',inputevents_cv.charttime) = '2105-12'