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: CONCLUSION : Although the natural occurrence of YMDD motif mutants in lamivudine - untreated patients with chronic hepatitis B has been reported , these mutants were not detected in Iranian lamivudine - untreated chronic hepatitis B patients .
### Output Text:
CONCLUSION : Although the natural occurrence of YMDD motif mutants in <span class="chemical">lamivudine</span> - untreated patients with chronic hepatitis B has been reported , these mutants were not detected in Iranian <span class="chemical">lamivudine</span> - untreated chronic hepatitis B patients . 