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.Collections.Generic;
using System.Linq;
using System;

namespace bla2
{
    class Program
    {
        static void Main()
        {
            string[] s = Console.ReadLine().Split();
            int n = int.Parse(s[0]);
            int k = int.Parse(s[1]);
            List<long> x = Console.ReadLine().Split().ToList().ConvertAll(long.Parse);
            List<long> neg = new List<long>();
            List<long> pos = new List<long>();
            int i;
            for (i = 0; i < x.Count && x[i] < 0; i++)
            {
                neg.Add(-x[i]);
            }
            if (i < x.Count)
            {
                if (x[i] == 0) { k--; i++; }
                for (; i < x.Count; i++)
                {
                    pos.Add(x[i]);
                }
            }
            neg.Reverse();
            if (k <= 0) { Console.WriteLine(0); return; }
            long best = long.MaxValue;
            if(k <= pos.Count) best = pos[k - 1];
            if (k <= neg.Count) best = Math.Min(best, neg[k - 1]);
            if (neg.Count != 0 && pos.Count != 0)
            {
                for (int j = 1; j < k; j++)
                {
                    if (j - 1 >= pos.Count) break;
                    if (k - j < 1) break;
                    if (k - j - 1 >= neg.Count) continue;
                    best = Math.Min(best, pos[j - 1] * 2 + neg[k - j - 1]);
                }
                for (int j = 1; j < k; j++)
                {
                    if (j - 1 >= neg.Count) break;
                    if (k - j < 1) break;
                    if (k - j - 1 >= pos.Count) continue;
                    best = Math.Min(best, neg[j - 1] * 2 + pos[k - j - 1]);
                }
            }
            Console.WriteLine(best);
        }
    }
}