Exhibit

We have audited the consolidated financial statements included in the Form 10-K and issued our report thereon dated February 22, 2019. Note 2 to the financial statements describes a change in accounting principle for recognizing stock-based compensation expense from the graded method of expense attribution to the straight-line method of expense attribution for stock-based compensation awards subject only to a time-based service vesting condition. It should be understood that the preferability of one acceptable method of accounting over another for recognition of stock-based compensation expense for awards with service conditions only has not been addressed in any authoritative accounting literature, and in expressing our concurrence below we have relied on management’s determination that this change in accounting principle is preferable. Based on our reading of management’s stated reasons and justification for this change in accounting principle in the Form 10-K, and our discussions with management as to their judgment about the relevant business planning factors relating to the change, we concur with management that such change represents, in the Company’s circumstances, a change to a preferable accounting principle in conformity with Accounting Standards Codification 250, Accounting Changes and Error Corrections.