You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(4-ethoxyphenyl)-N-[2-[3-(4-methylphenyl)-1,2,4-oxadiazol-5-yl]ethyl]acetamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H23N3O3
assistant