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: The median number of bort - dex cycles was 6 , up to a maximum of 12 cycles .
### Output Text:
The median number of <span class="chemical">bort</span> - <span class="chemical">dex</span> cycles was 6 , up to a maximum of 12 cycles . 