; except that no individual under conviction for crime and serving sentence therefore shall be employed under the provisions of this Act. 4. Authorization of appropriations (a) Authorization of appropriations There are authorized to be appropriated to the President $16,000,000,000 for each of fiscal years 2018 through 2021 to establish and operate a Civilian Conservation Corps under this Act. (b) Use of unobligated funds appropriated for public works (1) Use of existing funds The President may use any moneys previously appropriated for public works and unobligated as of the date of the enactment of this Act to establish and operate a Civilian Conservation Corps under this Act. (2) Use to relieve unemployment Not less than 80 percent of the funds utilized pursuant to paragraph (1) must be used to provide for the employment of individuals under this Act. (3) Exceptions Paragraph (1) does not apply to— (A) unobligated moneys appropriated for public works on which actual construction has been commenced as of the date of the enactment of this Act or may be commenced within 90 days after that date; and (B) maintenance funds for river and harbor improvements already allocated as of the date of the enactment of this Act. (c) Duration of availability Amounts appropriated pursuant to the authorization of appropriations in subsection (a) or made available under subsection (b) shall remain available until expended. 5. Termination The authority of the President to establish and operate a Civilian Conservation Corps under this Act expires on September 30, 2021.