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: Animals treated only with 5 - FU showed significant deficits in their ability to carry out the OLR task but co administration of Fluoxetine improved their performance .
### Output Text:
Animals treated only with <span class="chemical">5 - FU</span> showed significant deficits in their ability to carry out the OLR task but co administration of <span class="chemical">Fluoxetine</span> improved their performance . 