You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(4-chlorophenyl)-N-[2-(3-cyclopropyl-5-oxo-4-phenyl-1,2,4-triazol-1-yl)ethyl]acetamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H21ClN4O2
assistant