You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[4-(difluoromethoxy)-3-[(2,4-difluorophenyl)methyl]-2-ethyl-8-fluoroquinolin-5-yl]oxyacetic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H16F5NO4
assistant