what was the dosage of warfarin that was last prescribed to patient 69895 in the last hospital visit?
select prescriptions.dose_val_rx from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 69895 and admissions.dischtime is not null order by admissions.admittime desc limit 1 ) and prescriptions.drug = 'warfarin' order by prescriptions.startdate desc limit 1