You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 1-[4-(2,5-difluorophenyl)sulfonylpiperazin-1-yl]-4-(4-nitroanilino)butan-1-one by IUPAC nomenclature, provide its molecular formula.
user
C20H22F2N4O5S
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