what was the last value of patient 45612's laboratory test for potassium in 05/2101?
select labevents.valuenum from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 45612 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'potassium' ) and strftime('%y-%m',labevents.charttime) = '2101-05' order by labevents.charttime desc limit 1