You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Translate the chemical IUPAC name (9E)-9-benzylidene-3-(2-chloroethyl)-2-methyl-7,8-dihydro-6H-pyrido[1,2-a]pyrimidin-4-one into its molecular formula.
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C18H19ClN2O
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