You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[(3R)-3-[5-(5-ethyl-1,2,4-oxadiazol-3-yl)pyrimidin-4-yl]pyrrolidin-1-yl]-(2-methoxy-3-methylphenyl)methanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H23N5O3
assistant