You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
8-(3-fluoropyridin-4-yl)-2-[(3-methoxyphenyl)methyl]-2,8-diazaspiro[4.5]decan-3-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H24FN3O2
assistant