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;

namespace ARC101C
{
    class Program
    {
        static void Main(string[] args)
        {
            long[] longs = Console.ReadLine().Split(' ').Select(a => long.Parse(a)).ToArray();
            long N = longs[0];
            long K = longs[1];
            long[] V = Console.ReadLine().Split(' ').Select(a => long.Parse(a)).ToArray();

            long leftLength = 1;
            long rightLength = 1;
            for (long i = 0; i < N; i++)
            {
                if (V[i] < 0)
                {
                    leftLength++;
                }
                if (V[i] >= 0)
                {
                    rightLength++;
                }
            }
            long[] left = new long[leftLength];
            left[0] = 0;
            for (long i = 1; i < leftLength; i++)
            {
                left[i] = V[leftLength - i - 1];
            }

            long[] right = new long[rightLength];
            right[0] = 0;
            for (long i = 1; i < rightLength; i++)
            {
                right[i] = V[N - rightLength + i];
            }


            long min = Int64.MaxValue;
            
            for (long i = 0; i < K + 1; i++)
            {
                if (K - i >= right.Length | K - i < 0 | i >= left.Length)
                {
                    continue;
                }
                min = Math.Min(min, -left[i] + right[K - i] * 2);
                min = Math.Min(min, -left[i] * 2 + right[K - i]);
            }
            Console.WriteLine(min);
        }
    }
}