You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Please write the molecular formula of the molecule (3E,11bR)-3-[2-(4-chlorophenyl)-2-oxoethylidene]-2,6,7,11b-tetrahydro-1H-pyrazino[2,1-a]isoquinolin-4-one .
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C20H17ClN2O2
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