Problem:
Score : 300 points

Problem Statement

There are N candles placed on a number line.
The i-th candle from the left is placed on coordinate x_i.
Here, x_1 < x_2 < ... < x_N holds.

Initially, no candles are burning.
Snuke decides to light K of the N candles.

Now, he is at coordinate 0.
He can move left and right along the line with speed 1.
He can also light a candle when he is at the same position as the candle, in negligible time.

Find the minimum time required to light K candles.

Constraints

1 \leq N \leq 10^5

1 \leq K \leq N

x_i is an integer.

|x_i| \leq 10^8

x_1 < x_2 < ... < x_N

Input

Input is given from Standard Input in the following format:

N K
x_1 x_2 ... x_N

Output

Print the minimum time required to light K candles.

Sample Input 1

5 3
-30 -10 10 20 50

Sample Output 1

40

He should move and light candles as follows:

Move from coordinate 0 to -10.

Light the second candle from the left.

Move from coordinate -10 to 10.

Light the third candle from the left.

Move from coordinate 10 to 20.

Light the fourth candle from the left.

Sample Input 2

3 2
10 20 30

Sample Output 2

20

Sample Input 3

1 1
0

Sample Output 3

0

There may be a candle placed at coordinate 0.

Sample Input 4

8 5
-9 -7 -4 -3 1 2 3 4

Sample Output 4

10

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Linq;//リストの使用
using System.Collections.Generic;
class Program
{
	static void Main()
	{
	string[] input = Console.ReadLine().Split(' ');//Splitで区切り文字を指定して複数個受け取る。
	long n = long.Parse(input[0]);
	long k = long.Parse(input[1]);
	long[] nums = Array.ConvertAll(Console.ReadLine().Split(' '),long.Parse);
  long answer = long.MaxValue;

    for(long i = 0; i < n+1-k; i++)
    {
      long a = Math.Abs(nums[i]);
      long b = Math.Abs(nums[i+k-1]);
      long c = Math.Min(2*a+b, 2*b+a);
      answer = Math.Min(answer, c);
    }

  	Console.WriteLine(answer);//WriteLineをWriteとすると、改行なしで出力。
	}
}