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: Concurrent treatment of both dietary groups with Warfarin produced massive focal calcification of the artery media in the ad libitum - fed rats but no detectable artery calcification in the restricted - diet , growth - inhibited group .
### Output Text:
Concurrent treatment of both dietary groups with <span class="chemical">Warfarin</span> produced massive focal calcification of the artery media in the ad libitum - fed rats but no detectable artery calcification in the restricted - diet , growth - inhibited group . 