You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Under IUPAC nomenclature, a molecule named (7E)-3-(4-acetylphenyl)-7-(5-bromo-2-oxo-1H-indol-3-ylidene)-2,4-dihydro-[1,3]thiazolo[3,2-a][1,3,5]triazin-6-one is given. What is its corresponding molecular formula?
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C21H15BrN4O3S
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