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: STUDY OBJECTIVE : Chest pain in the setting of cocaine use poses a diagnostic dilemma .
### Output Text:
STUDY OBJECTIVE : Chest pain in the setting of <span class="chemical">cocaine</span> use poses a diagnostic dilemma . 