; or (2) the number of communications collected under such section to which a party is a person inside the United States. (b) In case of technical impossibility If the Director determines that publishing an estimate pursuant to subsection (a) is not technically possible— (1) subsection (a) shall not apply; and (2) the Director shall publish an assessment in unclassified form explaining such determination, but may submit a classified annex to the appropriate committees of Congress as necessary. (c) Appropriate committees of Congress defined In this section, the term appropriate committees of Congress means— (1) the congressional intelligence committees (as defined in section 3 of the National Security Act of 1947 ( 50 U.S.C. 3003 )); (2) the Committee on the Judiciary of the Senate ; and (3) the Committee on the Judiciary of the House of Representatives . 19. Four-year extension of FISA Amendments Act of 2008 (a) Extension Section 403(b) of the FISA Amendments Act of 2008 ( Public Law 110–261 ) is amended— (1) in paragraph (1) (50 U.S.C. 1881–1881g note), by striking December 31, 2017 and inserting September 30, 2021 ; and (2) in paragraph (2) ( 18 U.S.C. 2511 note), in the material preceding subparagraph (A), by striking December 31, 2017 and inserting September 30, 2021 . (b) Conforming amendment The heading of section 404(b)(1) of the FISA Amendments Act of 2008 ( Public Law 110–261 ; 50 U.S.C. 1801 note) is amended by striking December 31, 2017 and inserting September 30, 2021 .