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: Low - dose haloperidol did not differ from placebo on any measure of efficacy or side effects .
### Output Text:
Low - dose <span class="chemical">haloperidol</span> did not differ from placebo on any measure of efficacy or side effects . 