You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule N-[4-[3-(4-hydroxy-9-oxa-2-azaspiro[5.5]undecan-2-yl)-3-oxopropyl]phenyl]prop-2-enamide into molecular formula.
user
C21H28N2O4
assistant