You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[2-[1-[(2-chloro-6-fluorophenyl)methyl]benzimidazol-2-yl]ethyl]-4-hydroxybutanamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H21ClFN3O2
assistant