tell me the monthly minimum amount of tpn d13.5 in patient 26469's body since 04/2105?
select min(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 = 26469 ) ) and inputevents_cv.itemid in ( select d_items.itemid from d_items where d_items.label = 'tpn d13.5' and d_items.linksto = 'inputevents_cv' ) and strftime('%y-%m',inputevents_cv.charttime) >= '2105-04' group by strftime('%y-%m',inputevents_cv.charttime)