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: BACKGROUND : Most patients presenting to emergency departments ( EDs ) with cocaine - associated chest pain are admitted for at least 12 hours and receive a " rule out acute coronary syndrome " protocol , often with noninvasive testing prior to discharge .
### Output Text:
BACKGROUND : Most patients presenting to emergency departments ( EDs ) with <span class="chemical">cocaine</span> - associated chest pain are admitted for at least 12 hours and receive a " rule out acute coronary syndrome " protocol , often with noninvasive testing prior to discharge . 