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.Linq;

namespace Candles
{
    class Program
    {
        static void Main(string[] args)
        {
            var nk = GetArrayIntInput();
            var inputs = GetArrayIntInput();

            var list = inputs.OrderBy(Math.Abs).Take(nk[1]).ToList();
            list.Sort();
            var range = Math.Abs(list[0] - list[list.Count - 1]);
            var moveDistance1 = range + Math.Abs(list[0]);
            var moveDistance2 = range + Math.Abs(list[list.Count - 1]);
            CWrite(moveDistance1 < moveDistance2 ? moveDistance1 : moveDistance2);
        }

        static string[] GetArrayCharInput() => Console.ReadLine().Split();
        static int[] GetArrayIntInput() => Console.ReadLine().StringToIntArray();
        static int GetIntInput() => Console.ReadLine().ToInt();
        static void CWrite<T>(T str) => Console.WriteLine(str);
    }

    static class ExtentionsLibrary
    {
        public static int[] StringToIntArray(this string str) =>
            str.Split().Select(int.Parse).ToArray();
        public static int ToInt(this string str) => int.Parse(str);
    }
}