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 (4aR)-10-(2-phenylethyl)-2,3,4,4a,5,6-hexahydro-1H-pyrazino[2,1-d][1,5]benzoxazepine into molecular formula.
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C20H24N2O
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