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: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;

namespace ABC107C
{
    class MainClass
    {
        public static void Main(string[] args)
        {


            string[] input1 = Console.ReadLine().Split(' ');
            int N = int.Parse(input1[0]);
            int K = int.Parse(input1[1]);
 

            // L,R(M) 電車の両端
            // これはi + 1の値が入ってくるので注意
            int[] x = new int[N];
            string[] input2;


            input2 = Console.ReadLine().Split(' ');

            bool isPlus = true;
            int plusNum = -1;
            for (int i = 0; i < N; i++)
            {
                x[i] = int.Parse(input2[i]);
                if(isPlus && x[i] >= 0){
                    plusNum = i;
                    isPlus = false;
                }
            }


            List<int> ans = new List<int>();
            if(plusNum == -1){
                //正の値なし
                //左にKこある
                Console.WriteLine(Math.Abs(x[N - K]));
                return;


            }
            if( K -1 <= plusNum && K <= N - plusNum){
                //左にKこあり、右にもKこある
                for (int i = plusNum - K + 1; i <= plusNum; i++)
                {


                    if (i + K - 1 < plusNum)
                    {
                        //すべて負
                        ans.Add(Math.Abs(x[i]));
                    }
                    else if (i >= plusNum)
                    {
                        //すべて正
                        ans.Add(Math.Abs(x[i + K - 1]));
                    }
                    else if (Math.Abs(x[i]) >= x[i + K - 1])
                    {
                        //正のが近い
                        ans.Add(Math.Abs(x[i]) + 2 * Math.Abs(x[i + K - 1]));
                    }
                    else
                    {
                        //負のが近い
                        ans.Add(2 * Math.Abs(x[i]) + Math.Abs(x[i + K - 1]));
                    }
                }

            }else if(K - 1 <= plusNum ){
                //左にKこある
                for (int i = plusNum - K+ 1; i < N-K +1; i++)
                {
                    if (i + K - 1 < plusNum)
                    {
                        //すべて負
                        ans.Add(Math.Abs(x[i]));
                    }
                    else if (i >= plusNum)
                    {
                        //すべて正
                        ans.Add(Math.Abs(x[i + K - 1]));
                    }
                    else if (Math.Abs(x[i]) >= x[i + K - 1])
                    {
                        //正のが近い
                        ans.Add(Math.Abs(x[i]) + 2 * Math.Abs(x[i + K - 1]));
                    }
                    else
                    {
                        //負のが近い
                        ans.Add(2 * Math.Abs(x[i]) + Math.Abs(x[i + K - 1]));
                    }
                }
                
            }else if(K <= N - plusNum){
                //右にKこある
                for (int i = 0; i <= plusNum; i++)
                {
                    if (i + K - 1 < plusNum)
                    {
                        //すべて負
                        ans.Add(Math.Abs(x[i]));
                    }
                    else if (i >= plusNum)
                    {
                        //すべて正
                        ans.Add(Math.Abs(x[i + K - 1]));
                    }
                    else if (Math.Abs(x[i]) >= x[i + K - 1])
                    {
                        //正のが近い
                        ans.Add(Math.Abs(x[i]) + 2 * Math.Abs(x[i + K - 1]));
                    }
                    else
                    {
                        //負のが近い
                        ans.Add(2 * Math.Abs(x[i]) + Math.Abs(x[i + K - 1]));
                    }
                }

            }else{
                //両側Kこ未満
                for (int i = 0; i < N - K + 1; i++)
                {
                    if (i + K - 1 < plusNum)
                    {
                        //すべて負
                        ans.Add(Math.Abs(x[i]));
                    }
                    else if (i >= plusNum)
                    {
                        //すべて正
                        ans.Add(Math.Abs(x[i + K - 1]));
                    }
                    else if (Math.Abs(x[i]) >= x[i + K - 1])
                    {
                        //正のが近い
                        ans.Add(Math.Abs(x[i]) + 2 * Math.Abs(x[i + K - 1]));
                    }
                    else
                    {
                        //負のが近い
                        ans.Add(2 * Math.Abs(x[i]) + Math.Abs(x[i + K - 1]));
                    }
                }
            }

            Console.WriteLine(ans.Min());


        }
    }

}