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 abc107_c
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] nums = Console.ReadLine().Split(' ');
            int n = int.Parse(nums[0]);
            int k = int.Parse(nums[1]);
            int[] x = new int[100001];
            int sign_bound = 0;

            nums = Console.ReadLine().Split(' ');

            for(int i = 0; i < n; ++i)
            {
                x[i] = int.Parse(nums[i]);
            }

            int min_t = 1 << 30;

            for(int i = 0; i < n - k + 1; ++i)
            {
                int t;
                int l = x[i];
                int r = x[i + k - 1];

                if (l >= 0)
                {
                    t = r;
                }
                else if (r <= 0)
                {
                    t = -l;
                }
                else if (-l < r)
                {
                    t = 2 * -l + r;
                }
                else
                {
                    t = -l + 2 * r;
                }

                if(t < min_t)
                {
                    min_t = t;
                }
            }

            Console.WriteLine(min_t);
        }
    }
}