when patient 17667 got his arterial bp mean measured for the last time since 08/20/2105?
select chartevents.charttime from chartevents where chartevents.icustay_id in ( select icustays.icustay_id from icustays where icustays.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 17667 ) ) and chartevents.itemid in ( select d_items.itemid from d_items where d_items.label = 'arterial bp mean' and d_items.linksto = 'chartevents' ) and strftime('%y-%m-%d',chartevents.charttime) >= '2105-08-20' order by chartevents.charttime desc limit 1