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: Risk of transient hyperammonemic encephalopathy in cancer patients who received continuous infusion of 5 - fluorouracil with the complication of dehydration and infection .
### Output Text:
Risk of transient hyperammonemic encephalopathy in cancer patients who received continuous infusion of <span class="chemical">5 - fluorouracil</span> with the complication of dehydration and infection . 