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 9-(3-methyl-1,3,4,6,7,8,9,9a-octahydropyrido[1,2-a]pyrazin-2-yl)nonane-1-thiol into molecular formula.
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C18H36N2S
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