You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named (5E)-5-[[7-methyl-4-oxo-2-(prop-2-enylamino)pyrido[1,2-a]pyrimidin-3-yl]methylidene]-3-prop-2-enyl-2-sulfanylidene-1,3-thiazolidin-4-one by IUPAC nomenclature, provide its molecular formula.
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C19H18N4O2S2
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