calculate how many times oxymetazoline was prescribed to patient 88191 on their first hospital encounter.
select count(*) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 88191 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and prescriptions.drug = 'oxymetazoline'