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;

class Program
{
    static void Main(string[] args)
    {
        string[] input = Console.ReadLine().Split();
        int N = int.Parse(input[0]);
        int K = int.Parse(input[1]);
        input= Console.ReadLine().Split();
        int[] x = new int[N];
        for (int i = 0; i <N ; i++)
        {
            x[i] = int.Parse(input[i]);
        }
        int ans = int.MaxValue, temp = 0;
        for(int i =0; i <= N-K; i++)
        {
            temp=Math.Min(Math.Abs(x[i])+Math.Abs(x[i+K-1]-x[i]), Math.Abs(x[i + K - 1]) + Math.Abs(x[i + K - 1] - x[i]));
            ans = Math.Min(ans, temp);
        }
        Console.WriteLine(ans);
    }
}