what is patient 31306's yearly maximum white blood cells level since 41 months ago?
select max(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 31306 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'white blood cells' ) and datetime(labevents.charttime) >= datetime(current_time,'-41 month') group by strftime('%y',labevents.charttime)