You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[[(3aR,4S,7R,7aR)-2-(2-bromophenyl)-7-methyl-1,3-dioxo-3a,7a-dihydro-4,7-epoxyisoindol-4-yl]-acetyloxymethyl] acetate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H18BrNO7
assistant