tell me the dose of ns (syringe) that patient 30267 was prescribed in their last hospital encounter?
select sum(prescriptions.dose_val_rx) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 30267 and admissions.dischtime is not null order by admissions.admittime desc limit 1 ) and prescriptions.drug = 'ns (syringe)'