You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 4-[4-(benzenesulfonyl)piperazin-1-yl]-N-[(1,5-dimethylpyrrol-2-yl)methyl]-4-oxobutanamide into its molecular formula.
user
C21H28N4O4S
assistant