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: Increased frequency and severity of angio - oedema related to long - term therapy with angiotensin - converting enzyme inhibitor in two patients .
### Output Text:
Increased frequency and severity of angio - oedema related to long - term therapy with <span class="chemical">angiotensin - converting enzyme inhibitor</span> in two patients . 