You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (2R)-N-(2,5-dichlorophenyl)-2-[4-(4-methylphenyl)sulfonylpiperazin-1-yl]propanamide by IUPAC nomenclature, provide its molecular formula.
user
C20H23Cl2N3O3S
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