what was the number of patients who had been prescribed potassium chl 40 meq / 1000 ml d5w in 2103?
select count( distinct admissions.subject_id ) from admissions where admissions.hadm_id in ( select prescriptions.hadm_id from prescriptions where prescriptions.drug = 'potassium chl 40 meq / 1000 ml d5w' and strftime('%y',prescriptions.startdate) = '2103' )