You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Provide the molecular formula for the IUPAC named substance 4-chloro-1-(3-methyl-1,3,4,6,7,8,9,9a-octahydropyrido[1,2-a]pyrazin-2-yl)butan-1-one .
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C13H23ClN2O
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