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 (3S)-3-methyl-N-[(2-methylpyridin-3-yl)methyl]-3,4-dihydro-1H-isoquinoline-2-carboxamide is given. What is its corresponding molecular formula?
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C18H21N3O
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