You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named N-[2-[(2'S,3R)-2'-(1-methylpyrazol-4-yl)-2-oxospiro[1H-indole-3,3'-pyrrolidine]-1'-yl]-2-oxoethyl]methanesulfonamide by IUPAC nomenclature, provide its molecular formula.
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C18H21N5O4S
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