You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[2-(5-ethyl-1,3,4-oxadiazol-2-yl)pyrrol-1-yl]-N-(2-ethylphenyl)acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H20N4O2
assistant