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: BACKGROUND : Methamphetamine is a very addictive , powerful stimulant that increases wakefulness and physical activity and can produce other effects such as cardiac dysrhythmias , hypertension , hallucinations , and violent behavior .
### Output Text:
BACKGROUND : <span class="chemical">Methamphetamine</span> is a very addictive , powerful stimulant that increases wakefulness and physical activity and can produce other effects such as cardiac dysrhythmias , hypertension , hallucinations , and violent behavior . 