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;
class Program{
	static void Main(){
		int[] s=Array.ConvertAll(Console.ReadLine().Split(),int.Parse);
		int[] a=Array.ConvertAll(Console.ReadLine().Split(),int.Parse);
		int z=0,b=0,c=1<<30;
		if(s[0]==1){ }
		else if(a[0]==0){}
		else if(a[0]>0){
			s[0]++;
			Array.Resize(ref a,a.Length+1);
			for(int j=s[0]-1;j>0;j--){a[j]=a[j-1];}
			a[0]=0;
			z=0;
			s[1]++;
		}
		else if(a[s[0]-1]==0){}
		else if(a[s[0]-1]<0){
			s[0]++;
			Array.Resize(ref a,a.Length+1);
			a[s[0]-1]=0;
			z=s[0]-1;
			s[1]++;
		}
		else{
			for(int i=0;i<s[0]-1;i++){
				if(a[i]==0){break;}
				else if(a[i]<0&&a[i+1]>0){
					s[0]++;
					Array.Resize(ref a,a.Length+1);
					for(int j=s[0]-1;j>i;j--){a[j]=a[j-1];}
					a[i+1]=0;
					z=i+1;
					s[1]++;
					break;
				}
			}
		}

		for(int i=Math.Max(0,z-s[1]+1);i<s[0]&&i+s[1]-1<s[0];i++){
			b=Math.Abs(a[i]-a[i+s[1]-1]);
			if(a[i]!=0&&a[i+s[1]-1]!=0){
				b+=Math.Min(Math.Abs(a[z]-a[i]),Math.Abs(a[z]-a[i+s[1]-1]));
			}
			c=Math.Min(c,b);
		}
		if(s[0]==1){c=Math.Abs(a[0]);}
		Console.WriteLine("{0}",c);
	}
}