You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule N-[1-(2-chlorophenyl)-3-(3,4-dihydro-2H-1,5-benzoxazepin-5-yl)-3-oxopropyl]acetamide into molecular formula.
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C20H21ClN2O3
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