what is the average total cost of a hospital that includes a medicine called heparin flush since 2102?
select avg(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 = 'heparin flush' ) and strftime('%y',cost.chargetime) >= '2102' group by cost.hadm_id ) as t1