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

            long output = long.MaxValue;
            for (int i = 0; i+K < N+1; i++)
            {
                long hidari = x[i];
                long migi = x[i + K-1];
                long candidate = long.MaxValue;
                if (hidari * migi > 0)
                {
                    if(Math.Max(Math.Abs(hidari), Math.Abs(migi)) <candidate)
                    candidate = Math.Max(Math.Abs(hidari), Math.Abs(migi));
                }
                else
                {
                    if(Math.Abs(hidari) + migi + Math.Min(migi, Math.Abs(hidari))<candidate)
                    candidate = Math.Abs(hidari) + migi + Math.Min(migi, Math.Abs(hidari));
                }
                if (output > candidate) output = candidate;
            }
            Console.WriteLine(output);
        }
    }
}