You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (3S)-3-[(1-acetyl-2,3-dihydroindol-5-yl)sulfonyl]-1-(azepan-1-yl)butan-1-one by IUPAC nomenclature, provide its molecular formula.
user
C20H28N2O4S
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