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,min,i,left,right;
	scanf("%d %d",&N,&K);
	int x[N];
	for(i=0;i<N;i++) scanf("%d",&x[i]);
	
	min=2*abs(x[0])+2*abs(x[N-1]);
	
	for(i=0;i<=N-K;i++){
		left=x[i],right=x[K-1+i];
		if(left*right>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);
}