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)

// デバッグ実行：Ctrl+F5

using System;

class Program
{
    static void Main(string[] args)
    {
        String line;
        line = Console.ReadLine();
        String[] words = line.Split(' ');
        int N,K;
        int[] rousoku;
        N = int.Parse(words[0]);
        K = int.Parse(words[1]);

        rousoku = new int[N];
        line = Console.ReadLine();
        words = line.Split(' ');
        for (int i = 0; i < N; i++)
        {
            rousoku[i] = int.Parse(words[i]);
        }
        int min = 100000000;
        int kouho = 0;
        int x1, x2;
        if (K == 1)
        {
            for (int i = 0; i < N; i++)
            {
                kouho = Math.Abs(rousoku[i]);
                if (min > kouho)
                {
                    min = kouho;
                }
            }
        }
        else
        {
            for(int i = 0; i < N-K; i++)
            {
                x1 = Math.Abs(rousoku[i]);
                x2 = Math.Abs(rousoku[i + K - 1]);
                if (rousoku[i] < 0 && rousoku[i + K - 1] < 0)
                {
                    kouho = x1;
                }
                else if (rousoku[i] >= 0 && rousoku[i + K - 1] >= 0)
                {
                    kouho = x2;
                }
                else
                {
                    if (x1 > x2)
                    {
                        kouho = x1 + x2 * 2;
                    }
                    else
                    {
                        kouho = x1 * 2 + x2;
                    }
                }

                if (min > kouho)
                {
                    min = kouho;
                }
            }
        }
        Console.WriteLine(min);

    }
}