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-bromo-1-methyl-N'-[(1S)-2-oxo-1-phenyl-2-pyrrolidin-1-ylethyl]pyrrole-2-carbohydrazide into molecular formula.
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C18H21BrN4O2
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