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

public class Remainder
{
    static long N;
    static long K;
    static public void Main ()
    {
        var NK = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();
        N = NK[0];
        K = NK[1];
        var X = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();
        
        var LeftLi  = new List<long>();
        var RightLi = new List<long>();
        
        for(int i = 0;i < N;i++){
            if(X[i] >= 0){
                RightLi.Add(X[i]);
            }else{
                LeftLi.Add(-1*X[i]);
            }
        }
        
        var Left  = LeftLi.ToArray();
        var Right = RightLi.ToArray();
        var ans = long.MaxValue;
        
        for(int i = Right.Length;i >= 0;i--){
            
            
            var L = 0L;
            var R = 0L;
            var res = 0L;
            
            if(i >= 1){
                R = Right[i-1];
                
            }
           
            if((K-i) >= 1){
                if((K-i-1) < Left.Length){
                L = Left[Left.Length-1-(K-i-1)];
                res = Math.Min(L,R);
                }else{
                    break;
                }
                
            }
            res += (L+R);
            if(res < ans){
                ans = res;
            }
        }
        
        Console.WriteLine(ans);

    }

}