You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Provide the molecular formula for the IUPAC named substance (1S,15R,18S,19S,20S)-19-(hydroxymethyl)-1,3,11,12,14,15,16,17,18,19,20,21-dodecahydroyohimban-18-ol .
user
C20H26N2O2
assistant