You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4-[2-[5-chloro-7-(oxan-4-ylmethylamino)-1H-indol-2-yl]ethyl]piperazin-2-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H27ClN4O2
assistant