You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Under IUPAC nomenclature, a molecule named 3H-benzimidazol-5-yl-(1-methylsulfonylspiro[2H-indole-3,4'-piperidine]-1'-yl)methanone is given. What is its corresponding molecular formula?
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C21H22N4O3S
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