link : http://mirror.codeforces.com/gym/100548 My n^6 tree dp with constant optimal get Accepted. I think this problem's float point accuracy is harder than algorithm....it will take more effort to get "within an absolute error of 10−6" than thinking algorithm.....

using long double with some heuristic compute, my code's last example acurracy error is 8e-7.... dangerous Accepted...