You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the molecule identified by (1R,2R,4S,5S,8S,9S,10S,11R)-4,5-dihydroxy-11-methyl-6-methylidene-12-oxo-13-oxapentacyclo[9.3.3.15,8.01,10.02,8]octadecane-9-carboxylic acid ?
user
C20H26O6
assistant