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 algorithm
{
	class Program
	{

		static void Main(string[] args)
		{
			//全体/必要本数
			var q = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
			//座標
			var b = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
			q[1]--;
			//末端の近さ
			
			//0から近い端を調べる
			int str = Math.Min(b[0],b[q[1]]);
			int end = Math.Max(b[0], b[q[1]]);
			int cost = Math.Abs(str) +Math.Abs(end)+ Math.Min(Math.Abs(str),Math.Abs(end));
			int tmp = 0;
			for (int i =0;i<q[0]-q[1]; i++)
			{
				str = Math.Min(b[i], b[q[1]+i]);
				end = Math.Max(b[i], b[q[1]+i]);
				tmp = Math.Abs(str) + Math.Abs(end) + Math.Min(Math.Abs(str), Math.Abs(end));
				cost = Math.Min(tmp, cost);

			}
			
			//出力
			Console.WriteLine(cost);
			Console.ReadLine();
		}
	}
}