You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named (3aR,9bR)-2-[3-(3,5-dimethylpyrazolidin-4-yl)propanoyl]-1,3,4,9b-tetrahydrochromeno[3,4-c]pyrrole-3a-carboxylic acid by IUPAC nomenclature, provide its molecular formula.
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C20H27N3O4
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