You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 17-but-3-enyl-4,12-dichloro-8,16,17-triazatetracyclo[7.7.1.02,7.010,15]heptadeca-2(7),3,5,10(15),11,13-hexaene by IUPAC nomenclature, provide its molecular formula.
user
C18H17Cl2N3
assistant