You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
methyl-[(13S,14S)-13-methyl-15-methylidene-17-oxo-7,11,12,14-tetrahydro-6H-cyclopenta[a]phenanthren-3-yl]sulfamic acid The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H23NO4S
assistant