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: Sixty - two patients ( 88 . 6 % ) are alive with functioning grafts 686 + / - 362 days ( range , 154 - 1433 days ) after conversion .
### Output Text:
Sixty - two patients ( 88 . 6 % ) are alive with functioning grafts 686 + / - 362 days ( range , 154 - 1433 days ) after conversion . 