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.Linq;

namespace ABC107C_cs2
{
    class Program
    {
        static void Main(string[] args)
        {
            var nx = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            var arrayx = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            var t = new Candles(nx[0], nx[1], arrayx);
            Console.WriteLine(t.MinTime());
        }
    }
    public class Candles
    {
        private readonly int N;
        private readonly int K;

        public int MinTime()
        {
            int result = int.MaxValue;
            for (int i = 0; i < N - K + 1; i++)
            {
                int LeftIndex = i;
                int RightIndex = i + K - 1;
                int LeftRoundTime = Math.Abs(arrayx[LeftIndex]) + Math.Abs(arrayx[LeftIndex] - arrayx[RightIndex]);
                int RightRoudnTime = Math.Abs(arrayx[RightIndex]) + Math.Abs(arrayx[LeftIndex] - arrayx[RightIndex]);
                result = Math.Min(Math.Min(LeftRoundTime, RightRoudnTime), result);
            }
            return result;
        }

        private readonly int[] arrayx;

        public Candles(int v1, int v2, int[] v3)
        {
            this.N = v1;
            this.K = v2;
            this.arrayx = v3;
        }
    }
}