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 (4aR,10aR)-5,6-dihydroxy-7-[(2S)-1-hydroxypropan-2-yl]-1,1,4a-trimethyl-3,4,10,10a-tetrahydro-2H-phenanthren-9-one .
user
C20H28O4
assistant