You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (1R,5S,6R,7S)-3-methyl-6-(1,3,4,5-tetrahydropyrido[4,3-b]indole-2-carbonyl)-10-oxa-3-azatricyclo[5.2.1.01,5]dec-8-en-4-one by IUPAC nomenclature, provide its molecular formula.
user
C21H21N3O3
assistant