You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[2-[5-(4-chlorophenyl)-1,2,4-oxadiazol-3-yl]ethyl]-N-methylnaphthalene-2-sulfonamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H18ClN3O3S
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