You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(1S,2R,10S,11S,15S)-2,15-dimethyl-8-methylidenepentacyclo[8.7.0.02,7.05,7.011,15]heptadecane The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H30
assistant