Second answer ①, second answer

Second answer ①, second answer

05: pi

Total time limit: 1000 ms

Memory limit: 65536kB

It's my birthday! According to the customs, I need to distribute some to you. I have N schools of different tastes and sizes. There are F friends who will come to my party and each person will get a school (one school is required, not a small piece of pie; it can be a whole school ).

My friends are very stingy. If someone gets a bigger part, they will start to complain. Therefore, all people get the same size (but do not need to be in the same shape). Although some of them will be wasted, it is better than messing up the entire party. Of course, I also want to leave a piece for myself, which is the same size as other people.

What is the maximum number of school members each of us receives? Each faction is a cylinder with a height of 1 and a radius. The first line of the input contains two positive integers N and F, 1 ≤ N, F ≤ 10 000, indicating the number of friends and the number of friends. The second row contains N integers ranging from 1 to 10000, indicating the radius of each pie.

Output

Output the maximum volume that each person can obtain, accurate to three digits after the decimal point.

Input 3 3 4 3 Output 25.133

[Idea] At the beginning, I did not expect a binary answer, although these questions are of the binary answer type.

Each person can score the largest or infinitely small area in all units (this is the answer range). The condition of the card answer is whether the score can be obtained, obviously, the answer is a binary answer. Therefore, the question of the binary answer is a direct question. The maximum value of the question is a binary answer, however, for a relatively invisible question, you should first look at the characteristics of the answer. 1. You can determine the answer range. 2. conditions with a card answer. orz [Code]