tell me the maximum hospital cost that includes cholecystectomy in 2105?
select max(t1.c1) from ( select sum(cost.cost) as c1 from cost where cost.hadm_id in ( select procedures_icd.hadm_id from procedures_icd where procedures_icd.icd9_code = ( select d_icd_procedures.icd9_code from d_icd_procedures where d_icd_procedures.short_title = 'cholecystectomy' ) ) and strftime('%y',cost.chargetime) = '2105' group by cost.hadm_id ) as t1