You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
6,8-dihydroxy-7-[3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]-4,4a-dihydroxanthene-2,3,9-trione The above is the IUPAC name of a molecule. Write its molecular formula.
user
C19H18O11
assistant