You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(4-chloro-5-fluoro-1-methylindazol-3-yl)-1-(5-methyl-2-azatricyclo[3.3.1.13,7]decan-2-yl)propan-1-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H25ClFN3O
assistant