You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule 3,7,9-trihydroxy-17-methyl-16,18-dioxapentacyclo[15.2.2.02,15.04,13.06,11]henicosa-2(15),3,6(11),7,9,13-hexaene-5,12-dione .
user
C20H16O7
assistant