I've got WA again and again.
I've tested my program on a lot of different tests.

But I'm not sure in accuracy of calculations...
Is it 10E-10 or 10E-100 or some other ?

And may the room's size (2000x2000) influence on the
result?

And may any two points in the input be the same ?

THANKS.

I can't find any mistake in my program.

But the questions remains:

1. Must I check the solution on conditons:
             -1000 <= x1,x2 <= 1000
             -1000 <= y1,y2 <= 1000
    ??????
   the text of the problem is ambiguous here.

2. Can the arc cross the walls of the hall ?

3. Can two (or three) points in the input be the same.
   (the problem didn't tell about it)

> I can't find any mistake in my program.
>
> But the questions remains:
>
> 1. Must I check the solution on conditons:
>              -1000 <= x1,x2 <= 1000
>              -1000 <= y1,y2 <= 1000
>     ??????
>    the text of the problem is ambiguous here.
There is no contradiction.
>
> 2. Can the arc cross the walls of the hall ?

The arc - cannot, but circle of this angle - can..

> 3. Can two (or three) points in the input be the same.
>    (the problem didn't tell about it)
>
No

And, about precision - the answer is INTEGER!

> And, about precision - the answer is INTEGER!
I know.

And one more question:
Can the radius of the circle be equal to eternity (can all
three points lie on the same line) ?

Thank you.

> And one more question:
> Can the radius of the circle be equal to eternity (can
all
> three points lie on the same line) ?

No. Center of the circle is inside of hall.
Read the problem text carefully :^)

Oh, yea !
I've got accept !

Thank you.