Could somebody who solved this problem give some tests to me? WA #7 :(

Also asking for some random tests, because it's hard to check the solution.

random test:
25 7 3
4.0671982122

good luck =)

thanks 1 y

100 2 20
0.00000

100 98 1
0.12311156

85 17 53
2.1738219