An investment pays you, only in even years, a dollar amount equals to the number of years from today. That is, $2 at the end of year 2, $4 at the end of year 4, $6 at the end of year 6, $8 at the end of year 8, $10 at the end of year 10, and so on forever. In addition, you will receive $20 every ten years forever. Find the present value of this investment today if the discount rate is 10% (per year).