You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2,2-dimethylbicyclo[2.2.1]heptane;2,2-dimethylbicyclo[2.2.2]octane;1,2,2,7,7-pentamethylbicyclo[2.2.1]heptane is the IUPAC name of a molecule. Please give its molecular formula.
user
C31H56
assistant