You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name methyl (2R,3R,3aS,9bS)-3-(hydroxymethyl)-1-methylsulfonyl-6-oxo-7-phenyl-3,3a,4,9b-tetrahydro-2H-pyrrolo[2,3-a]indolizine-2-carboxylate into its molecular formula.
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C20H22N2O6S
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