You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[2-(2,4-dichlorophenyl)ethyl]-3-(3-methylphenyl)-1-(1H-pyrrol-2-ylmethyl)urea The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H21Cl2N3O
assistant