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: Frequency of absences increased in four children treated with carbamazepine and two of these developed myoclonic jerks , which resolved on withdrawal of carbamazepine .
### Output Text:
Frequency of absences increased in four children treated with <span class="chemical">carbamazepine</span> and two of these developed myoclonic jerks , which resolved on withdrawal of <span class="chemical">carbamazepine</span> . 