You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 3-[2-[4-(2-chlorophenyl)piperazin-1-yl]-2-oxoethyl]-6-thiophen-2-ylpyrimidin-4-one into its molecular formula.
user
C20H19ClN4O2S
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