You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(4R)-3-oxapentacyclo[9.8.0.02,4.05,10.013,18]nonadeca-1(19),5,7,9,11,13,15,17-octaene is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H12O
assistant