You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (4aR,5R,5aR,12aS)-2-acetyl-5,6,10,12a-tetrahydroxy-6-(hydroxymethyl)-4a,5,5a,11a-tetrahydro-4H-tetracene-1,3,11,12-tetrone by IUPAC nomenclature, provide its molecular formula.
user
C21H20O10
assistant