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)

#pragma warning disable

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.Serialization.Formatters.Binary;
using System.Text;
using System.Text.RegularExpressions;
using System.Diagnostics;
using System.Numerics;
using System.Collections;

static class MainClass
{
    public static void Main(string[] args)
    {
        var nk = Console.ReadLine().SplittedStringToInt32List();
        var n = nk[0];
        var k = nk[1];
        var xn = Console.ReadLine().SplittedStringToInt32List();
        var minusind = xn.FindIndex(x => x >= 0);
        var minsum = Int32.MaxValue;
        if (minusind == 0)
        {
            minsum = xn[k - 1];
        }
        else
        { 
            for (int i = 0; i <= minusind; i++)
            {
                var sum = 0;
                if (i + k - 1 < n)
                {
                    sum += Math.Abs(xn[i]) * 2 + xn[i + k - 1];
                    minsum = Math.Min(minsum, sum);
                }
            }
        }
        Console.WriteLine(minsum);

        Console.ReadLine();
        //var nm = Console.ReadLine().SplittedStringToInt32List();
        //var n = nm[0];
        //var m = nm[1];
        //InitializeUnionFind(n);
        //var abs = new List<KeyValuePair<int,int>>();
        //for (int i = 0; i < m; i++)
        //{
        //    var ab = Console.ReadLine().SplittedStringToInt32List();
        //    abs.Add(new KeyValuePair<int, int>(ab[0] - 1, ab[1] - 1));
        //}
        //abs.Reverse();
        //var ls = new List<int>();
        //foreach (var item in abs)
        //{
        //    Unite(item.Key, item.Value);
        //    ls.Add(ParentCount);
        //}
        //ls.Reverse();
        //var before = -1;
        //var befores = 0;
        //for (int i = 0; i < m; i++)
        //{
        //    if (before != -1)
        //    {
        //        var num = ls[i] - befores;
        //        Console.WriteLine((num * (num - 1))/2 + before);
        //        before = (num * (num - 1)) / 2 + before;
        //    }
        //    else
        //    {
        //        var num = ls[i] - befores;
        //        Console.WriteLine((num * ( num - 1)) / 2);
        //        before = (num * (num - 1)) / 2;
        //    }
        //    befores = ls[i];
        //}

        //Console.ReadLine();

    }


    public static List<List<int>> NBasedSearch(int n, int length)
    {
        if (length == 1)
        {
            var ls = new List<List<int>>();
            for (int i = 0; i < n; i++)
            {
                var lss = new List<int>();
                lss.Add(i);
                ls.Add(lss);
            }
            return ls;
        }
        else
        {
            var ans = NBasedSearch(n, length - 1);
            var news = new List<List<int>>();
            foreach (var item in ans)
            {
                for (int i = 0; i < n; i++)
                {
                    var based = item.ToList();
                    based.Add(i);
                    news.Add(based);
                }
            }
            return news;

        }
    }

    public static long Guchokukai(long k,List<long> ls)
    {
        var max = -1l;
        for (long i = 0; i <= k; i++)
        {
            var sum = 0l;
            foreach (var item in ls)
            {
                sum += item ^ i;
            }
            max = Math.Max(sum, max);
        }
        return max;
    }
    

    public static int ParentCount;

    public static int[] Parents;
    public static int[] IfParentsChildrenCount;

    public static int[] Ranks;

    public static void InitializeUnionFind(int N)
    {
        Parents = new int[N];
        Ranks = new int[N];
        IfParentsChildrenCount = new int[N];
        for (int i = 0; i < N; i++)
        {
            Parents[i] = i;
            Ranks[i] = 0;
            IfParentsChildrenCount[i] = 1;
        }
        ParentCount = N + 1;
    }

    public static int Root(int a)
    {
        if (Parents[a] == a)
        {
            return a;
        }
        else
        {
            Parents[a] = Root(Parents[a]);
            return Parents[a];
        }
    }

    public static bool Same(int a, int b)
    {
        return Root(a) == Root(b);
    }

    public static void Unite(int a, int b)
    {
        var parentA = Root(a);
        var parentB = Root(b);
        if (parentA == parentB)
            return;
        if (Ranks[parentA] < Ranks[parentB])
        {
            Parents[parentA] = parentB;
            IfParentsChildrenCount[parentB] += IfParentsChildrenCount[parentA];
            ParentCount -= IfParentsChildrenCount[parentA];

            IfParentsChildrenCount[parentA] = 0;
        }
        else
        {
            Parents[parentB] = parentA;
            if (Ranks[parentA] == Ranks[parentB])
            {
                Ranks[parentA]++;
            }
            IfParentsChildrenCount[parentA] += IfParentsChildrenCount[parentB];
            ParentCount -= IfParentsChildrenCount[parentB];
            IfParentsChildrenCount[parentB] = 0;
        }
    }

    #region ライブラリ
    public static long ToInt64(this string str) => long.Parse(str);
    public static int ToInt32(this string str) => str == "" ? 0 : int.Parse(str);
    public static BigInteger ToBigInteger(this string str) => BigInteger.Parse(str);
    public static List<string> SplittedStringToList(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).ToList();
    public static List<int> SplittedStringToInt32List(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => int.Parse(x)).ToList();
    public static List<long> SplittedStringToInt64List(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => long.Parse(x)).ToList();
    public static List<BigInteger> SplittedStringToBigInteger(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => BigInteger.Parse(x)).ToList();
    public const int INF = int.MaxValue / 4;
    public const long LONGINF = long.MaxValue / 2;
    public const int Mod1e9 = 1000000007;

    public static void PrintArray(bool[,] array)
    {
        for (int i = 0; i < array.GetLength(0); i++)
        {
            var sb = new StringBuilder();
            for (int j = 0; j < array.GetLength(1); j++)
            {
                sb.Append(array[i, j]).Append(" ");
            }
            Console.WriteLine(sb.ToString());
        }
    }
    public static int Manhattan(int x1, int x2, int y1, int y2)
    {
        return Math.Abs(x1 - x2) + Math.Abs(y1 - y2);
    }

    public static Dictionary<T, int> ToCountedDictionary<T>(this IEnumerable<T> items)
    {
        var dic = new Dictionary<T, int>();
        foreach (var item in items)
        {
            if (dic.ContainsKey(item))
                dic[item]++;
            else
                dic.Add(item, 1);
        }
        return dic;
    }

    public static long Sums(IEnumerable<int> list)
    {
        var sum = 0l;
        foreach (var item in list)
        {
            sum += item;
        }
        return sum;
        #endregion
    }
}