You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(4-ethoxyphenyl) 2-[[5-(1H-indol-3-yl)-1,3,4-oxadiazol-2-yl]sulfanyl]acetate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H17N3O4S
assistant