You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[2-[4-(2-hydroxyphenyl)piperazin-1-yl]-2-oxoethyl]-3-phenylimidazolidin-2-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H24N4O3
assistant