A company has a copper mine which is expected to be mined indefinitely. The current copper price is 100 yuan / ton, the annual output is 20000 tons, and the annual operating cost is 3 million yuan. Suppose that in the next two years, the copper price will rise or fall by 20% each year(the probability is 50% equally), and then it will remain at that level. Set the cost of capital at 12%.

1. Calculate the net present value of the continued operation of copper mines