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: Neural correlates of S - ketamine induced psychosis during overt continuous verbal fluency .
### Output Text:
Neural correlates of <span class="chemical">S - ketamine</span> induced psychosis during overt continuous verbal fluency . 