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: PATIENTS AND METHODS : From February , 1998 to September , 2000 we recruited 33 patients with AGC to receive weekly 24 - hour 5 - FU 2 , 600 mg / m ( 2 ) preceded by 2 - hour FA 500 mg / m ( 2 ) for 6 weeks , followed by a 2 - week rest period .
### Output Text:
PATIENTS AND METHODS : From February , 1998 to September , 2000 we recruited 33 patients with AGC to receive weekly 24 - hour <span class="chemical">5 - FU</span> 2 , 600 mg / m ( 2 ) preceded by 2 - hour <span class="chemical">FA</span> 500 mg / m ( 2 ) for 6 weeks , followed by a 2 - week rest period . 