CUSIP No. 42217K106 13G Page 9 of 9 Pages

Exhibit A to Schedule 13G

Joint Filing Agreement
Pursuant to Rule 13d-1(k)

        The undersigned persons (the “Reporting Persons”) hereby agree that a joint statement on this Schedule 13G, and any amendments thereto, be filed on their behalf by ING Groep N.V.

        Each of the Reporting Persons is responsible for the completeness and accuracy of the information concerning each of them contained therein, but none of the Reporting Persons is responsible for the completeness or accuracy of the information concerning any other Reporting Person.

Date:  August 14, 2008

ING GROEP N.V.
By:	/s/ Eric E. Ribbers
	Name:  Eric E. Ribbers
	Title:    Senior Compliance Officer
By:	/s/ R.M. Fischmann
	Name:  R.M. Fischmann
	Title:    Head of Compliance, Regulator & Industry Body
ING CLARION REAL ESTATE SECURITIES, L.P.
By:	/s/ William Zitelli
	Name:  William Zitelli
	Title:    Chief Compliance Officer