You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(3S)-8-[4-(difluoromethoxy)benzoyl]-2-methyl-2,8-diazaspiro[4.5]decane-3-carboxylic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H22F2N2O4
assistant