in 02/2105, what was the minimum osmolality, measured value for patient 89673?
select min(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 89673 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'osmolality, measured' ) and strftime('%y-%m',labevents.charttime) = '2105-02'