You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named 2-(2-chloro-3-prop-2-enylbenzimidazol-1-ium-1-yl)-1-(4-methylphenyl)ethanone;bromide by IUPAC nomenclature, provide its molecular formula.
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C19H18BrClN2O
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