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: Faster relief of headache was the most important reason for preference , cited by 67 . 3 % of patients preferring rizatriptan and 54 . 2 % of patients who preferred ergotamine / caffeine .
### Output Text:
Faster relief of headache was the most important reason for preference , cited by 67 . 3 % of patients preferring <span class="chemical">rizatriptan</span> and 54 . 2 % of patients who preferred <span class="chemical">ergotamine</span> / <span class="chemical">caffeine</span> . 