You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4-methyl-2-[3-(2-methylpropyl)-4-(2-nitrophenyl)sulfonyl-2-oxopiperazin-1-yl]pentanoic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H29N3O7S
assistant