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: RESULTS : All five patients experienced symptoms of encephalopathy soon after ( within 12 h - 2 days ) receiving ifosfamide .
### Output Text:
RESULTS : All five patients experienced symptoms of encephalopathy soon after ( within 12 h - 2 days ) receiving <span class="chemical">ifosfamide</span> . 