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: Cyclical low - dose oestrogen therapy with 7 - - 13 days of progestagen does not seem to increase the risk of endometrial hyperplasia or carcinoma .
### Output Text:
Cyclical low - dose <span class="chemical">oestrogen</span> therapy with 7 - - 13 days of <span class="chemical">progestagen</span> does not seem to increase the risk of endometrial hyperplasia or carcinoma . 