how much insulin human regular was prescribed to patient 40435 since 03/2104, for the first time?
select prescriptions.dose_val_rx from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 40435 ) and prescriptions.drug = 'insulin human regular' and strftime('%y-%m',prescriptions.startdate) >= '2104-03' order by prescriptions.startdate asc limit 1