You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[(4S)-3,4-dihydro-2H-chromen-4-yl]-4-(1,3-dioxoisoindol-2-yl)butanamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H20N2O4
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