Thank you! But it's very strange. I found the radius using bin search. The right border for search was the sum of all lengths - it must be greater than radius. And I've got WA 14. After changing right border to 10^6 I've got AC.
If you try to check a very big radius, the parameter of arcsin gets very low. I assume the function just returns its parameter if it's very close to 0 but your eps needs to be very low as well.
Also, the raduis of a polygon's circumscribed circle can be infinitely large no matter what's the upper boundary for its sides is. In this problem, there is a lower boundary too, so you can actually limit your binary search with something.