You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name (4E)-4-[(5-ethyl-2-methoxyphenyl)methylidene]-2-[2-(2-fluorophenyl)ethyl]-1H-imidazol-5-one into its molecular formula.
user
C21H21FN2O2
assistant