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;
using System.Text;
class Program
{
    static void Main(string[] args)
    {
            // 入力
            string[] sS = System.Console.ReadLine().Trim().Split(' ');
            int iN = int.Parse(sS[0]);
            int iK = int.Parse(sS[1]);
            List<ClsPos> lstPos = new List<ClsPos>();
            sS = System.Console.ReadLine().Trim().Split(' ');
            for (int i = 0; i < sS.Length; i++)
            {
                ClsPos oneUsr = new ClsPos();
                oneUsr.iD = i;                                  // Index
                oneUsr.iX = int.Parse(sS[i]);                   // X 位置
                oneUsr.iZ = Math.Abs(oneUsr.iX);                // 絶対位置
                lstPos.Add(oneUsr);
            }
            //// Debug入力
            //int iN = 100000;
            //int iK = 99999;
            //List<ClsPos> lstPos = new List<ClsPos>();
            //for (int i = 0; i < iN; i++)
            //{
            //    ClsPos oneUsr = new ClsPos();
            //    oneUsr.iD = i;                                  // Index
            //    oneUsr.iX = -50000 + i;                         // X 位置
            //    oneUsr.iZ = Math.Abs(oneUsr.iX);                // 絶対位置
            //    lstPos.Add(oneUsr);
            //}

            System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch();
            sw.Start();

            // 解析
            lstPos.Sort(delegate (ClsPos mca1, ClsPos mca2) { return (int)(mca1.iZ - mca2.iZ); });      // iZでの昇順
            List<ClsPos> lstOut = new List<ClsPos>();
            for (int i = 0; i < iK; i++)                        // 0 から近いiKまで
            {
                ClsPos oneUsr = new ClsPos();
                oneUsr.iD = lstPos[i].iD;                       // Index
                oneUsr.iX = lstPos[i].iX;                       // X 位置
                oneUsr.iZ = lstPos[i].iZ;                       // 絶対位置
                lstOut.Add(oneUsr);
            }
            lstOut.Sort(delegate (ClsPos mca1, ClsPos mca2) { return (int)(mca1.iD - mca2.iD); });      // iDでの昇順
            long iOut = 0;
            if (lstOut[0].iX < 0 && lstOut[lstOut.Count - 1].iX > 0)    // Minus方向Plus方向両方あり
            {
                if (lstOut[0].iZ < lstOut[lstOut.Count - 1].iZ) { iOut += lstOut[0].iZ * 2 + lstOut[lstOut.Count - 1].iZ; }     // 最初移動方向Minus
                else { iOut += lstOut[0].iZ + lstOut[lstOut.Count - 1].iZ * 2; }                                                // 最初移動方向Plus
            }
            else if (lstOut[0].iX >= 0)                                 // Plus方向のみ
            {
                iOut += lstOut[lstOut.Count - 1].iZ;
            }
            else if (lstOut[lstOut.Count - 1].iX <= 0)                  // Minus方向のみ
            {
                iOut += lstOut[0].iZ;
            }

            // 出力
            System.Console.WriteLine("{0}", iOut.ToString().Trim());

            sw.Stop();
#if DEBUG
            Console.WriteLine();
            Console.WriteLine("{0}", sw.Elapsed.ToString());
            Console.WriteLine("続行するには何かキーを押してください．．．");
            Console.ReadKey();
#endif
    }

        // 情報
        private class ClsPos
        {
            public int iD { get; set; } = 0;                    // Index
            public int iX { get; set; } = 0;                    // X 位置
            public int iZ { get; set; } = 0;                    // 絶対位置
        }

}