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;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        var inputs = Console.ReadLine().Split(' ');
        var N = int.Parse(inputs[0]);
        var K = int.Parse(inputs[1]);
        inputs = Console.ReadLine().Split(' ');
        var x = new long[N];
        for (int i = 0; i < N; i++)
        {
            x[i] = long.Parse(inputs[i]);
        }

        long ans = 1000000000;
        for (int i = 0; i < N; i++)
        {
            if (i + K - 1 == N)
            {
                break;
            }
            var xl = x[i];
            var xr = x[i + K - 1];

            var leftToRight = Math.Abs(xl) + Math.Abs(xl - xr);
            var rightToLeft = Math.Abs(xr) + Math.Abs(xr - xl);
            var min = Math.Min(leftToRight, rightToLeft);
            ans = Math.Min(min, ans);
        }

        Console.WriteLine(ans);
    }
}