You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named tert-butyl 5-oxa-2,8-diazaspiro[3.5]nonane-2-carboxylate;8-methyl-5-oxa-2,8-diazaspiro[3.5]nonane by IUPAC nomenclature, provide its molecular formula.
user
C18H34N4O4
assistant