You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2R)-N-[(1S)-1-(3-fluoro-4-methoxyphenyl)ethyl]-2-(5-methyl-1,3-dioxoisoindol-2-yl)propanamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H21FN2O4
assistant