You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[(4S)-4-ethyl-2,5-dioxo-4-phenylimidazolidin-1-yl]-N-[(4-methoxyphenyl)methyl]acetamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H23N3O4
assistant