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: Wrong Answer)

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]);
                if (x[i] > 0 && first_flag == false)
                {
                    first_notminus = i;
                    first_flag = true;
                }

            }
            long minussum = 0;
            long plussum = 0;
            bool ok_minussum = true;
            bool ok_plussum = true;
            for (int i = 0; i< K; i++)
            {
                try
                {
                    minussum = x[first_notminus - 1 - i];
                }
                catch
                {
                    ok_minussum = false;
                }
                try
                {
                    plussum = x[first_notminus + i];

                }
                catch
                {
                    ok_plussum = false;
                }
            }
            long doublerun_minus = 0;
            long doublerun_plus = 0;
            int plus_number = 0;
            int minus_number = 0;

            bool plus_go = true;
            bool minus_go = true;
            for (int i = 0; i < K; i++)
            {
                long plus = 100000000;
                long minus = -100000000;
                try
                {
                     plus = x[first_notminus + plus_number];
                }
                catch
                {
                    plus_go = false;
                }
                try
                {
                     minus = x[first_notminus - 1 - minus_number];
                }
                catch
                {
                    minus_go = false;
                }
                if (Math.Abs(minus) >= plus && plus_go == true)
                {
                    doublerun_plus = plus;
                    plus_number++;
                }
                if (Math.Abs(minus) < plus && minus_go == true)
                {
                    doublerun_minus = Math.Abs(minus);
                    minus_number++;
                }
            }
            long winner = Math.Max(plussum, Math.Abs(minussum));
            if (ok_plussum == true && ok_minussum == false) winner = plussum;
            if (ok_plussum == false && ok_minussum == true) winner = Math.Abs(minussum);
            
            long seed = Math.Abs(doublerun_minus) + doublerun_plus + Math.Min(Math.Abs(doublerun_minus), doublerun_plus);

            if (ok_plussum == false && ok_minussum == false)
            {
                Console.WriteLine(seed);
            }
            else
            {
                Console.WriteLine(Math.Min(winner, seed));
            }
            
        }
    }
}