You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
5-oxaspiro[3.5]nonan-8-yl-[4-[4-(trifluoromethyl)phenyl]piperidin-1-yl]methanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H26F3NO2
assistant