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: Comparison of slow - wave sleep time , total sleep time , and sleep latency in cocaine - dependent and healthy participants revealed a normalizing effect of modafinil in cocaine - dependent participants .
### Output Text:
Comparison of slow - wave sleep time , total sleep time , and sleep latency in <span class="chemical">cocaine</span> - dependent and healthy participants revealed a normalizing effect of <span class="chemical">modafinil</span> in <span class="chemical">cocaine</span> - dependent participants . 