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 9.2.1) (judge verdict: Accepted)

#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

int main(void){
	int n, k, i;
	int x[100000];
	scanf("%d%d", &n, &k);
	for(i=0; i<n; i++){
		scanf("%d", x+i);
	}
	int l=n-k+1;
	int min=INT_MAX;
	for(i=0; i<l; i++){
		int now;
		if(x[i]>=0){
			now = x[i+k-1];
		}else if(x[i+k-1]<=0){
			now = -x[i];
		}else if(-x[i]<=x[i+k-1]){
			now = -x[i]*2 + x[i+k-1];
		}else{
			now = x[i+k-1]*2 - x[i];
		}
		if(now<min) min=now;
	}
	printf("%d\n", min);
}