Exhibit A

AGREEMENT TO FILE SCHEDULE 13D JOINTLY

(as required by Item 7 of Schedule 13D)

The undersigned persons hereby agree that reports on Schedule 13D, and any amendments thereto, may be filed in a single statement on behalf of all such persons, and further, each such person designates Warren E. Buffett as its agent and attorney-in-fact for the purpose of executing any and all such reports required to be made by it with the Securities and Exchange Commission.

Dated: August 11, 2017	/s/ Warren E. Buffett
	Warren E. Buffett
	Berkshire Hathaway Inc.
Dated: August 11, 2017	/s/ Warren E. Buffett
	By: Warren E. Buffett Title: Chairman of the Board
	National Indemnity Company
Dated: August 11, 2017	/s/ Marc D. Hamburg
	By: Marc D. Hamburg Title: Chairman of the Board
	GEICO Corporation
Dated: August 11, 2017	/s/ Stephen C. Parsons
	By: Stephen C. Parsons Title: Vice President
	Government Employees Insurance Company
Dated: August 11, 2017	/s/ Stephen C. Parsons
	By: Stephen C. Parsons Title: Vice President
	GEICO Indemnity Company
Dated: August 11, 2017	/s/ Stephen C. Parsons
	By: Stephen C. Parsons Title: Vice President
	GEICO Advantage Insurance Company
Dated: August 11, 2017	/s/ Stephen C. Parsons
	By: Stephen C. Parsons Title: Vice President
	GEICO Choice Insurance Company
Dated: August 11, 2017	/s/ Stephen C. Parsons
	By: Stephen C. Parsons Title: Vice President

	GEICO Secure Insurance Company
Dated: August 11, 2017	/s/ Stephen C. Parsons
	By: Stephen C. Parsons Title: Vice President
	GEICO Corporation Pension Plan Trust
Dated: August 11, 2017	/s/ Stephen C. Parsons
	By: Stephen C. Parsons Title: Vice President
	The Buffalo News Office Pension Plan
Dated: August 11, 2017	/s/ Warren Colville
	By: Warren Colville Title: President and Chief Executive Officer, The Buffalo News
	The Buffalo News Editorial Pension Plan
Dated: August 11, 2017	/s/ Warren Colville
	By: Warren Colville Title: President and Chief Executive Officer, The Buffalo News
	The Buffalo News Mechanical Pension Plan
Dated: August 11, 2017	/s/ Warren Colville
	By: Warren Colville Title: President and Chief Executive Officer, The Buffalo News
	The Buffalo News Drivers/Distributors Pension Plan
Dated: August 11, 2017	/s/ Warren Colville
	By: Warren Colville Title: President and Chief Executive Officer, The Buffalo News
	Berkshire Hathaway Consolidated Pension Plan Master Retirement Trust
Dated: August 11, 2017	/s/ Marc D. Hamburg
	By: Marc D. Hamburg Title: Senior Vice President, Berkshire Hathaway Inc.
	BNSF Master Retirement Trust
Dated: August 11, 2017	/s/ Julie Piggott
	By: Julie Piggott Vice President, Burlington Northern Santa Fe, LLC
	Johns Manville Corporation Master Pension Trust
Dated: August 11, 2017	/s/ Mary Rhinehart
	By: Mary Rhinehart Title: President and Chief Executive Officer, Johns Manville Corporation
	Acme Brick Company Pension Trust
Dated: August 11, 2017	/s/ Dennis Knautz
	By: Dennis Knautz Title: President and Chief Executive Officer, Acme Building Brands

	Scott Fetzer Company Collective Investment Trust
Dated: August 11, 2017	/s/ Robert McBride
	By: Robert McBride Title: President and Chief Executive Officer, Scott Fetzer Companies
	Lubrizol Master Trust Pension
Dated: August 11, 2017	/s/ Brian Valentine
	By: Brian Valentine Title: Vice President, The Lubrizol Corporation
	General Re Corporation Employee Trust
Dated: August 11, 2017	/s/ Michael O’Dea
	By: Michael O’Dea Title: Vice President, General Re Corporation
Dated: August 11, 2017	/s/ R. Ted Weschler
	R. Ted Weschler