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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
#include<math.h>
int main()
{
	int n,k,i,left,right;
	scanf("%d %d",&n,&k);
	int x[n+1];
	for(i=1;i<=n;i++){
		scanf("%d",&x[i]);
	}
	int min = 2*abs(x[1]) + 2*abs(x[n]);
	for(i=1;i<=n-k;i++){
		left = x[i];
		right = x[i+k-1];
		if(right<0||left>0){
			if(abs(left)>abs(right)){
				if(min>abs(left))min=abs(left);
			}else{
				if(min>abs(right))min=abs(right);
			}
		}else{
			if(min>2*abs(left)+abs(right))min=2*abs(left)+abs(right);
			if(min>abs(left)+2*abs(right))min=abs(left)+2*abs(right);
		}
	}
	printf("%d",min);
	return 0;
}