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: Acute confusion induced by a high - dose infusion of 5 - fluorouracil and folinic acid .
### Output Text:
Acute confusion induced by a high - dose infusion of <span class="chemical">5 - fluorouracil</span> and <span class="chemical">folinic acid</span> . 