tell me patient 24547's last urea nitrogen value in 09/2104?
select labevents.valuenum from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 24547 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'urea nitrogen' ) and strftime('%y-%m',labevents.charttime) = '2104-09' order by labevents.charttime desc limit 1