You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4-chloro-1-[2-[4-(4-chloro-3-methoxyphenyl)piperazin-1-yl]-2-oxoethyl]-5-methyl-N-propan-2-ylpyrazole-3-carboxamide is the IUPAC name of a molecule. Please give its molecular formula.
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C21H27Cl2N5O3
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