CUSIP No. 94419L101

Exhibit A

AGREEMENT REGARDING THE JOINT FILING OF

SCHEDULE 13D

The undersigned, being duly authorized thereunto, hereby execute this agreement as an exhibit to this Schedule 13D to evidence the agreement of the below-named parties, in accordance with the rules promulgated pursuant to the Securities Exchange Act of 1934, to file this Schedule jointly on behalf of each such party.

Date: February 17, 2015

Spark Capital III (AIV I), L.P.
	By:	Spark Management Partners III (AIV I), LLC
	By:	/s/ Paul Conway
		Authorized Signatory
Spark Capital Founders’ Fund III, L.P.
	By:	Spark Management Partners III, LLC
	By:	/s/ Paul Conway
		Authorized Signatory
Spark Management Partners III (AIV I), LLC
	By:	/s/ Paul Conway
		Authorized Signatory

CUSIP No. 15708Q105

Spark Management Partners III, LLC
	By:	/s/ Paul Conway
		Authorized Signatory
	/s/ Todd Dagres Todd Dagres
	/s/ Santo Politi Santo Politi
	/s/ Paul Conway Paul Conway
	/s/ Bijan Sabet Bijan Sabet
	/s/ Moshe Koyfman Moshe Koyfman
	/s/ Alexander J. Finkelstein Alexander J. Finkelstein