EXHIBIT 4

JOINT FILING AGREEMENT
PURSUANT TO RULE 13d-1(k)

The undersigned acknowledge and agree that the foregoing statement on Schedule 13D is filed on behalf of each of the undersigned and that all subsequent amendments to this statement on Schedule 13D shall be filed on behalf of each of the undersigned without the necessity of filing additional joint filing agreements. The undersigned acknowledge that each shall be responsible for the timely filing of such amendments, and for the completeness and accuracy of the information concerning him or it contained herein and therein, but shall not be responsible for the completeness and accuracy of the information concerning the others, except to the extent that he or it knows or has reason to believe that such information is inaccurate.

DATE: December 26, 2012

TPG-AXON MANAGEMENT LP

By: TPG-Axon GP, LLC, general partner

/s/ Dinakar Singh

Name:  Dinakar Singh

Title:    Chief Executive Officer

TPG-AXON GP, LLC

/s/ Dinakar Singh

Name:  Dinakar Singh

Title:    Chief Executive Officer

TPG-AXON PARTNERS GP, L.P.

By: TPG-Axon GP, LLC, general partner

/s/ Dinakar Singh

Name:  Dinakar Singh

Title:    Chief Executive Officer

TPG-AXON PARTNERS, LP

By: TPG-Axon Partners GP, L.P., general partner

By: TPG-Axon GP, LLC, general partner

/s/ Dinakar Singh

Name:  Dinakar Singh

Title:    Chief Executive Officer

TPG-AXON INTERNATIONAL GP, LLC

/s/ Dinakar Singh

Name:  Dinakar Singh

Title:    Chief Executive Officer

TPG-AXON INTERNATIONAL, L.P.

By: TPG-Axon International GP, LLC, general partner

/s/ Dinakar Singh

Name:  Dinakar Singh

Title:    Chief Executive Officer

DINAKAR SINGH LLC

/s/ Dinakar Singh

Name:  Dinakar Singh

Title:    Managing Member

/s/ Dinakar Singh

Dinakar Singh

/s/ Stephen C. Beasley

Stephen C. Beasley