how much is the maximum cost for a hospital that contains modafinil until 1 year ago?
select max(t1.c1) from ( select sum(cost.cost) as c1 from cost where cost.hadm_id in ( select prescriptions.hadm_id from prescriptions where prescriptions.drug = 'modafinil' ) and datetime(cost.chargetime) <= datetime(current_time,'-1 year') group by cost.hadm_id ) as t1