(5) (A) The amount of a monthly insurance benefit of any individual for each month under subsection (b), (c), (e), (f), or (g) (as determined after application of the provisions of subsection (q) and the preceding provisions of this subsection) shall be reduced (but not below zero) by an amount equal to two-thirds of the amount of any monthly periodic benefit payable to such individual for such month which is based upon such individual’s earnings while in the service of the Federal Government or any State (or political subdivision thereof, as defined in section 418(b)(2) of this title ) if, during any portion of the last 60 months of such service ending with the last day such individual was employed by such entity— (i) such service did not constitute “employment” as defined in section 410 of this title , or (ii) such service was being performed while in the service of the Federal Government, and constituted “employment” as so defined solely by reason of— (I) clause (ii) or (iii) of subparagraph (G) of section 410(a)(5) of this title , where the lump-sum payment described in such clause (ii) or the cessation of coverage described in such clause (iii) (whichever is applicable) was received or occurred on or after January 1, 1988 , or (II) an election to become subject to the Federal Employees’ Retirement System provided in chapter 84 of title 5 or the Foreign Service Pension System provided in subchapter II of chapter 8 of title I of the Foreign Service Act of 1980 [ 22 U.S.C. 4071 et seq.] made pursuant to law after December 31, 1987 , unless subparagraph (B) applies. The amount of the reduction in any benefit under this subparagraph, if not a multiple of $0.10, shall be rounded to the next higher multiple of $0.10. (B) (i) Subparagraph (A)(i) shall not apply with respect to monthly periodic benefits based wholly on service as a member of a uniformed service (as defined in section 410(m) of this title ). (ii) Subparagraph (A)(ii) shall not apply with respect to monthly periodic benefits based in whole or in part on service which constituted “employment” as defined in section 410 of this title if such service was performed for at least 60 months in the aggregate during the period beginning January 1, 1988 , and ending with the close of the first calendar month as of the end of which such individual is eligible for benefits under this subsection and has made a valid application for such benefits. (C) For purposes of this paragraph, any periodic benefit which otherwise meets the requirements of subparagraph (A), but which is paid on other than a monthly basis, shall be allocated on a basis equivalent to a monthly benefit (as determined by the Commissioner of Social Security) and such equivalent monthly benefit shall constitute a monthly periodic benefit for purposes of subparagraph (A). For purposes of this subparagraph, the term “periodic benefit” includes a benefit payable in a lump sum if it is a commutation of, or a substitute for, periodic payments.