You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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ethyl 7-(3,4-dichlorophenyl)-2-methyl-5-propyl-4,7-dihydro-[1,2,4]triazolo[1,5-a]pyrimidine-6-carboxylate is the IUPAC name of a molecule. Please give its molecular formula.
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C18H20Cl2N4O2
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