Section 20. Government Contribution.— As the contribution of the Government to the operation of the SSS, Congress shall annually appropriate out of any funds in the National Treasury not otherwise appropriated, the necessary sum or sums to meet the estimated expenses of the SSS for each ensuing year. In addition to this contribution, Congress shall appropriate from time 10 time such sum or sums as may be needed to assure the maintenance of an adequate working balance of the funds of the SSS as disclosed by suitable periodic actuarial studies to be made of the operations of the SSS.