what was the name of the drug that's been prescribed to patient 73713 two times during their first hospital visit?
select t1.drug from ( select prescriptions.drug, count( prescriptions.startdate ) as c1 from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 73713 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) group by prescriptions.drug ) as t1 where t1.c1 = 2