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;
using System.Text;

namespace Practice
{
    class Program
    {
        private static int ReadAndParseInt()
        {
            return int.Parse(Console.ReadLine());
        }
        private static int[] ReadAndParseIntArr()
        {
            return Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);
        }
        private static long ReadAndParseLong()
        {
            return long.Parse(Console.ReadLine());
        }
        private static long[] ReadAndParseLongArr()
        {
            return Array.ConvertAll(Console.ReadLine().Split(' '), long.Parse);
        }
        static void Main(string[] args)
        {
            SolveA(args);
            //SolveB(args);
            //SolveC(args);
            //SolveD(args);


        }

        static void SolveA(string[] args)
        {
            int[] nk = ReadAndParseIntArr();
            int n = nk[0];
            int k = nk[1];
            int[] x = ReadAndParseIntArr();

            long min = long.MaxValue;

            for(int left=0;left<x.Length;++left)
            {
                // ここからk本
                // パターン分け
                int right = left + k - 1;
                if(right >= x.Length) { break; }// 本数足りない

                if( x[right] < 0)
                {
                    // 左
                    min = Math.Min(min, -x[left]);
                }else if( x[left] > 0)
                {
                    // 右側
                    min = Math.Min(min, x[right]);
                }
                else
                {
                    // 原点を含む
                    // 右に行ってから左に折り返し
                    int dist = 2 * Math.Abs(x[right]) + Math.Abs(x[left]);
                    min = Math.Min(min, dist);
                    // 左行ってから右に折り返し 
                    dist = 2 * Math.Abs(x[left]) + Math.Abs(x[right]);
                    min = Math.Min(min, dist);
                }
            }

            Console.WriteLine(min);
        }
    }
}