You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
8-(4-chlorophenoxy)-2-[2-(4-fluorophenyl)-2-oxoethyl]-[1,2,4]triazolo[4,3-a]pyrazin-3-one is the IUPAC name of a molecule. Please give its molecular formula.
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C19H12ClFN4O3
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