when was patient 30614 last prescribed a medication using the po route in 12/2103?
select prescriptions.startdate from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 30614 ) and prescriptions.route = 'po' and strftime('%y-%m',prescriptions.startdate) = '2103-12' order by prescriptions.startdate desc limit 1