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: The number of affected valves ( n = 2 . 4 + / - 0 . 7 ) and the sum of regurgitation grades ( n = 2 . 8 + / - 1 . 09 ) were higher ( p = 0 . 008 and p = 0 . 006 , respectively ) in the pergolide group .
### Output Text:
The number of affected valves ( n = 2 . 4 + / - 0 . 7 ) and the sum of regurgitation grades ( n = 2 . 8 + / - 1 . 09 ) were higher ( p = 0 . 008 and p = 0 . 006 , respectively ) in the <span class="chemical">pergolide</span> group . 