Numbering duct

https://drive.google.com/file/d/0B7If7X6Nr6paemdWTTlraU1HUTA/view?usp=sharing

<span style=“color: #2e2e2e;”>Hi, </span><span style=“color: #212121;”>I need to enumerate for duct sections , to get the branch , how can I do it in the dynamo automatically , thanks in advance</span>