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: From June 2004 to October 2006 , 11 HBs Ag positive patients with rheumatologic diseases , who were on both immunosuppressive and prophylactic lamivudine therapies , were retrospectively assessed .
### Output Text:
From June 2004 to October 2006 , 11 <span class="chemical">HBs Ag</span> positive patients with rheumatologic diseases , who were on both immunosuppressive and prophylactic <span class="chemical">lamivudine</span> therapies , were retrospectively assessed . 