what was the last value of potassium of patient 22204 in 03/2103?
select labevents.valuenum from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 22204 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'potassium' ) and strftime('%y-%m',labevents.charttime) = '2103-03' order by labevents.charttime desc limit 1