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: High - dose 5 - fluorouracil / folinic acid infusion therapy has recently become a popular regimen for various cancers .
### Output Text:
High - dose <span class="chemical">5 - fluorouracil</span> / <span class="chemical">folinic acid</span> infusion therapy has recently become a popular regimen for various cancers . 