You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (2S)-1-[(2R)-2-(benzylsulfonylmethyl)-4-[(3S)-3-hydroxypyrrolidin-1-yl]-4-oxobutanoyl]pyrrolidine-2-carboxylic acid by IUPAC nomenclature, provide its molecular formula.
user
C21H28N2O7S
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