You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[5-(2-cyanoethoxycarbonyloxy)-2,6-dimethyl-4-(3-nitrophenyl)pyridin-3-yl] 2-cyanoethyl carbonate is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H18N4O8
assistant