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: Time Limit Exceeded)

#include<stdio.h>
#include<stdlib.h>
int main(){
	int n,k;
	scanf("%d %d",&n,&k);
	long x[n],ans=0;
	int i,j;
	for(i=0;i<n;i++)scanf("%ld",&x[i]);
	for(i=0;i<n;i++){
		for(j=0;j<n;j++){
			if(abs(x[i])<abs(x[j])){
			int tmp=x[i];
			x[i]=x[j];
			x[j]=tmp;
			}
			
			if(abs(x[i])==abs(x[j])){
				if(x[i]>0){
			int tmp=x[i];
			x[i]=x[j];
			x[j]=tmp;
			}
			}

		}
	}
	int sei=0,hu=0;
	ans+=abs(x[k-1]);
	for(i=0;i<k;i++){
		if(x[i]>0){
			if(sei<x[i])sei=x[i];
		}
		if(x[i]<0){
			if(hu>x[i])hu=x[i];
		}
	}
	if(sei!=0&&hu!=0){
		if(x[k-1]<0)ans+=2*abs(sei);
		if(x[k-1]>0)ans+=2*abs(hu);
	}
	printf("%ld\n",ans);
	//for(i=0;i<n;i++)printf("%ld,",x[i]);
	return 0;
}