In the condition it's said "accurate to 10−4", but in the examples the output contains much more digits.

It means that checker will take the difference of your answer and correct answer and if it less than 1e-4 than your answer is correct.
So you can display any number of digits. In my solution I display 10 digits after point

Ok, thanks for explanation. Nevertheless this is not the cause why i can't AC.
Can anybody say what trick is in the test #12?