what was the last time that patient 6440 had the maximum value of glucose since 12/2102?
select labevents.charttime from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 6440 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'glucose' ) and strftime('%y-%m',labevents.charttime) >= '2102-12' order by labevents.valuenum desc, labevents.charttime desc limit 1