You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[5-chloro-2-(4-methylpiperazin-1-yl)phenyl]-1-methyl-2-oxo-3H-indole-5-sulfonamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H23ClN4O3S
assistant