You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Convert the IUPAC name of a molecule (3aR)-4-methyl-9-oxo-N-(thiophen-2-ylmethyl)-1,2,3,3a-tetrahydropyrrolo[2,1-b]quinazoline-6-carboxamide into molecular formula.
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C18H19N3O2S
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