You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[4-[4-(4-chlorophenyl)-4-hydroxypiperidin-1-yl]butanoyl]-5-fluorobenzenediazonium;chloride is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H22Cl2FN3O2
assistant