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: OBJECTIVE : The goal of this study was to compare the efficacy and side effects of two doses of haloperidol and placebo in the treatment of psychosis and disruptive behaviors in patients with Alzheimer ' s disease .
### Output Text:
OBJECTIVE : The goal of this study was to compare the efficacy and side effects of two doses of <span class="chemical">haloperidol</span> and placebo in the treatment of psychosis and disruptive behaviors in patients with Alzheimer ' s disease . 