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: Recurrence rates were 31 . 4 % with rizatriptan and 15 . 3 % with ergotamine / caffeine .
### Output Text:
Recurrence rates were 31 . 4 % with <span class="chemical">rizatriptan</span> and 15 . 3 % with <span class="chemical">ergotamine</span> / <span class="chemical">caffeine</span> . 