You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Provide the molecular formula for the IUPAC named substance ethyl (2R,3S)-3-(4-chlorophenyl)-4-(2,4-dichlorophenyl)-2-(isocyanomethyl)piperazine-1-carboxylate .
user
C21H20Cl3N3O2
assistant