EXHIBIT 2

JOINT FILING AGREEMENT

The undersigned hereby agree to the joint filing of the Schedule 13D to which this Agreement is attached.

Dated: January 7, 2011

DISCOVERY GROUP I, LLC

By  Michael R. Murphy*                                   

Michael R. Murphy

Managing Member

Daniel J. Donoghue*                                         

Daniel J. Donoghue

Michael R. Murphy*                                         

Michael R. Murphy

*By: /s/ Mark Buckley                                       

         Mark Buckley

         Attorney-in-Fact for Daniel J. Donoghue

         Attorney-in-Fact for Michael R. Murphy