how much dapsone is prescribed to patient 95986 in total on the last hospital visit?
select sum(prescriptions.dose_val_rx) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 95986 and admissions.dischtime is not null order by admissions.admittime desc limit 1 ) and prescriptions.drug = 'dapsone'