how much atorvastatin is prescribed to patient 7698 a month before?
select sum(prescriptions.dose_val_rx) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 7698 ) and prescriptions.drug = 'atorvastatin' and datetime(prescriptions.startdate,'start of month') = datetime(current_time,'start of month','-1 month')