You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 1-[5-chloro-2-[4-[(3-methyl-1,2-oxazol-5-yl)methyl]piperazine-1-carbonyl]phenyl]pyrrolidin-2-one by IUPAC nomenclature, provide its molecular formula.
user
C20H23ClN4O3
assistant