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;
using System.Text;
using System.Threading.Tasks;

namespace ABC107C_cs
{
    class Program
    {
        static void Main(string[] args)
        {
            var nk = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            var x = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            var cdls = new Candles(nk[0], nk[1], x);
            Console.WriteLine(cdls.CalculateMinimumMoves());
        }
    }
    public class Candles
    {
        private int n;
        private int k;
        private int[] x;

        public Candles(int n, int k, int[] x)
        {
            this.n = n;
            this.k = k;
            this.x = x;
        }

        public int CalculateMinimumMoves()
        {
            var result = int.MaxValue;
            for(var cx = 0; cx < n - k + 1; cx++)
            {
                var left = x[cx];
                var right = x[cx + k - 1];
                var movelefttoright = Math.Abs(left) + Math.Abs(left - right);
                var moverighttoleft = Math.Abs(right) + Math.Abs(left - right);
                result = Math.Min(Math.Min(movelefttoright, moverighttoleft), result);
            }
            return result;
        }
    }
}