A borrows 20,000 from B and agrees to repay it with 20 equal annual installments of principal of 1000 plus the interest on the unpaid balance at 2% effective. After 10 years B sells the right to future payments to C, at a price which yields C a 5% effective over the next 5 years and 4% effective over the final 5 years. Find the price which C should pay to the nearest dollar.