You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2R)-N-[[3-(4-chlorophenyl)-1,2,4-oxadiazol-5-yl]methyl]-2-(N-methylsulfonylanilino)butanamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H21ClN4O4S
assistant