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>
#include <stdlib.h>

int min(int x,int y){
	return x<y? x: y;
}

int main(void){
	int N,K,ans=0,i,p;
	scanf("%d%d",&N,&K);
	int x[N],kouho[K];
	int set,left,right;
	for(i=0;i<N;i++){scanf("%d",&x[i]);}
	
	for(i=0;i<N-K+1;i++){
		set = 0;
		ans = 0;
		int j = i;
		while(set<K){//K個
			kouho[set] = x[j];
			set++;
			j++;
		}
		left = kouho[0];
		right = kouho[K-1];
		ans += min(abs(left),abs(right));
		for(int j=0;j<K-1;j++){
			ans += abs(kouho[j+1] - kouho[j]);
		}
		if(ans<p) p = ans;
	}
	
	
	printf("%d",p);
	
	return 0;
}