You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named propan-2-yl 5'-bromo-1'-(2,2-diethoxyethyl)-2'-oxospiro[azetidine-3,3'-indole]-1-carboxylate by IUPAC nomenclature, provide its molecular formula.
user
C20H27BrN2O5
assistant