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: Compared with placebo , modafinil decreased nighttime sleep latency and increased slow - wave sleep time in cocaine - dependent participants .
### Output Text:
Compared with placebo , <span class="chemical">modafinil</span> decreased nighttime sleep latency and increased slow - wave sleep time in <span class="chemical">cocaine</span> - dependent participants . 