You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(1-methylimidazol-2-yl)-1-[(1-phenyl-3-propan-2-ylpyrazol-4-yl)methyl]piperazine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H28N6
assistant