You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
potassium;cyclohexa-1,5-dien-1-ylmethylbenzene;[5-(methanidylideneamino)-1,2,3,6-tetrahydropyridin-4-yl]methanone The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H21KN2O-2
assistant