; (ii) in subparagraph (Y), by striking the period at the end and inserting ; and ; and (iii) by inserting after subparagraph (Y) the following new subparagraph: (Z) subject to paragraph (4), in the case of a hospital located in a county whose population density is above the median population density for all counties in the United States with respect to which there is a Herfindahl-Hirschman Index (HHI) of greater than 4,000, to apply the average reimbursement rate with respect to individuals (regardless of whether such an individual is entitled to or eligible for benefits under this title, but excluding individuals eligible for medical assistance under a State plan under title XIX) furnished items and services at such hospital that would be billable under this title for such items and services if furnished by such hospital to an individual enrolled under part C. ; and (B) by adding at the end the following new paragraph: (4) (A) The requirement under paragraph (1)(Z) shall not apply in the case of a hospital in a hospital referral region if— (i) the HRR market share of such hospital (as determined under subparagraph (B)) is less than 0.15