what's the daily maximum dose of po intake for patient 28020 until 182 days ago?
select max(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 = 28020 ) ) and inputevents_cv.itemid in ( select d_items.itemid from d_items where d_items.label = 'po intake' and d_items.linksto = 'inputevents_cv' ) and datetime(inputevents_cv.charttime) <= datetime(current_time,'-182 day') group by strftime('%y-%m-%d',inputevents_cv.charttime)