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 (4-nitrophenyl)methyl 2-chloro-2-[2-(3-ethyl-2,4-dioxopentan-3-yl)-4-oxoazetidin-1-yl]acetate into molecular formula.
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C19H21ClN2O7
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