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;


public class C{
	
	public static void Main(){
	
		string[] args1 = Console.ReadLine().Split(' ');
		int n = Int32.Parse(args1[0]);
		int k = Int32.Parse(args1[1]);
		int kp = k;
		
		string[] args2 = Console.ReadLine().Split(' ');
		int[] underZero = new int[n+1];
		underZero[0] = 0;
		int[] overZero = new int[n+1];
		overZero[0] = 0;
		int numUnderZero = 0;
		int numOverZero = 0;
		
		for( int i = 0; i < n; i++ ){
			
			int tmp = Int32.Parse(args2[i]);
			if( tmp < 0 ){
				numUnderZero++;
				underZero[numUnderZero] = -tmp;
				
			}else if( tmp == 0 ){
				kp = k - 1;
				
			}else{
				numOverZero++;
				overZero[numOverZero] = tmp;				
				
			}
			
		}
		Array.Reverse( underZero, 1, numUnderZero );
		
		int tmpMin = Int32.MaxValue;
		for( int i = 0; i <= kp; i++ ){
			
			if( i > numUnderZero ) continue;
			if( kp - i > numOverZero ) continue;
			
			int time;
			time = 2 * underZero[i] + overZero[kp - i];			
			if( time < tmpMin ) tmpMin = time;
			time = underZero[i] + 2 * overZero[kp - i];			
			if( time < tmpMin ) tmpMin = time;		
			
		}
		Console.WriteLine(tmpMin);
		
	}
	
}