You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[1-(2,4-dichloro-5-fluorophenyl)ethyl]-3-[(4-pyrrolidin-1-ylsulfonylphenyl)methyl]urea is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H22Cl2FN3O3S
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