In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: This finding points to the urgent need for evidence - based public health initiatives targeted at people who smoke crack cocaine .
### Output Text:
This finding points to the urgent need for evidence - based public health initiatives targeted at people who smoke <span class="chemical">crack cocaine</span> . 