You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-[3-(4-chlorophenyl)-1,2,4-oxadiazol-5-yl]-N-[2-[3-(difluoromethoxy)-4-methoxyphenyl]ethyl]propanamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H20ClF2N3O4
assistant