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;
using System.Collections.Generic;

namespace _20190605 {
  class ProblemC {
    static void Main(string[] args) {
      int[] vals = Input.nums;
      int[] x = Input.nums;
      int n = vals[0] - vals[1] + 1;
      int min = 0;
      min = Math.Min(Math.Abs(x[0]) + Math.Abs(x[vals[1] - 1] - x[0]), Math.Abs(x[vals[1] - 1]) + Math.Abs(x[vals[1] - 1] - x[0]));
      for (int i = 1; i < n; i++) {
        int tmp = Math.Min(Math.Abs(x[i]) + Math.Abs(x[vals[1] - 1 + i] - x[i]), Math.Abs(x[vals[1] - 1 + i]) + Math.Abs(x[vals[1] - 1 + i] - x[i]));
        if (tmp < min) {
          min = tmp;
        }
      }
      System.Console.WriteLine(min);
    }
  }
  public class Input {
    public static string str => System.Console.ReadLine();
    public static string[] strs => str.Split(' ');
    public static char[] charArr => str.ToCharArray();
    public static int num => int.Parse(str);
    public static int[] nums => Array.ConvertAll(strs, int.Parse);
    public static long numL => long.Parse(str);
    public static long[] numLs => Array.ConvertAll(strs, long.Parse);
  }
}