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.Collections.Generic;
using System.Linq;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            //[summary]C - Candles
            var line = ReadLine().ToList();
            int n = line[0];
            int k = line[1];

            var x = ReadLine().ToList();
            int min = int.MaxValue;

            for (int i = 0; i <= n - k; i++)
            {
                int firstX = x[i];
                int lastX = x[i + k - 1];

                int dist = GetDistance(firstX, lastX);

                if (dist < min)
                {
                    min = dist;
                }
            }

            Console.WriteLine(min);
        }

        static int GetDistance(int firstX, int lastX)
        {
            if (lastX < 0)
            {
                return Math.Abs(firstX);
            }
            else if (firstX > 0)
            {
                return lastX;
            }
            else
            {
                //片方の座標がマイナスで、もう片方がプラスのケース
                //(最初にどちらの方向に行くかで2パターンが考えられる)
                int dist1 = Math.Abs(firstX) * 2 + lastX;
                int dist2 = lastX * 2 + Math.Abs(firstX);

                if (dist1 > dist2)
                {
                    return dist1;
                }
                else
                {
                    return dist2;
                }
            }
        }

        static IEnumerable<int> ReadLine()
        {
            var line = Console.ReadLine().TrimEnd();
            var array = line.Split(' ');

            foreach (var s in array)
            {
                yield return int.Parse(s);
            }
        }
    }
}