You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named (3R,7aR)-N-(4,5-dichloropyridin-3-yl)-7a-methyl-5-oxo-2,3,6,7-tetrahydropyrrolo[2,1-b][1,3]thiazole-3-carboxamide by IUPAC nomenclature, provide its molecular formula.
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C13H13Cl2N3O2S
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