You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-(3-chloro-4-fluorophenyl)-2-(6-chloro-1,3,4,9-tetrahydropyrido[3,4-b]indol-2-yl)ethanol;formic acid The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H19Cl2FN2O3
assistant