You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[(5S)-4-[hydroxy-(4-methoxyphenyl)methylidene]-2,3-dioxo-5-phenylpyrrolidin-1-yl]acetic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H17NO6
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