Consider a pension plan that pays beneficiaries in the following manner: at the end of the retirement year of a beneficiary the value of all benefits are transferred to his or her personal account. This means that at the end of every year the pension plan makes lump-sum payments of pension benefits to its beneficiaries. The pension plan's actuarial team concluded that the pension's obligation stream could not be estimated beyond an 80-year horizon. They further estimate that the plan will have to make annual pension payments of $10 million per year throughout this 80-year horizon. The first payment will take place in exactly one year. Assume the current yield curve is flat at 6%.

What is the duration of the plan's expected obligation stream?