until September 30, 2021: Provided , That such funds shall be available to the Secretary of Defense for the purpose of allowing the Commander, Combined Security Transition Command—Afghanistan, or the Secretary's designee, to provide assistance, with the concurrence of the Secretary of State, to the security forces of Afghanistan, including the provision of equipment, supplies, services, training, facility and infrastructure repair, renovation, construction, and funding: Provided further , That the Secretary of Defense may obligate and expend funds made available to the Department of Defense in this title for additional costs associated with existing projects previously funded with amounts provided under the heading Afghanistan Infrastructure Fund in prior Acts: Provided further , That such costs shall be limited to contract changes resulting from inflation, market fluctuation, rate adjustments, and other necessary contract actions to complete existing projects, and associated supervision and administration costs and costs for design during construction: Provided further , That the Secretary may not use more than $50,000,000 under the authority provided in this section: Provided further , That the Secretary shall notify in advance such contract changes and adjustments in annual reports to the congressional defense committees: Provided further , That the authority to provide assistance under this heading is in addition to any other authority to provide assistance to foreign nations: Provided further , That contributions of funds for the purposes provided herein from any person, foreign government, or international organization may be credited to this Fund, to remain available until expended, and used for such purposes: Provided further , That the Secretary of Defense shall notify the congressional defense committees in writing upon the receipt and upon the obligation of any contribution, delineating the sources and amounts of the funds received and the specific use of such contributions: Provided further , That