What is the molecular formula of the molecule identified by 2-chloro-1-[(1R,2S,13S,14S,16S,17R,18S,20S)-6-ethyl-1-fluoro-17,20-dihydroxy-2,16,18-trimethyl-7-aza-6-azoniapentacyclo[11.7.0.02,10.04,8.014,18]icosa-5,7,9-trien-17-yl]ethanone ?