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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <algorithm>
using namespace std;
int h,k;
int main() {
	cin>>h>>k;
	int a[h],b[(h-k+1)],c[(h-k+1)];
	
	for(int i=0;i<h;i++){
		cin>>a[i];
	}
	for(int i=0;i+k-1<h;i+=1){
		b[i]=a[i+k-1]-a[i]+abs(a[i]);
		c[i]=a[i+k-1]-a[i]+abs(a[i+k-1]);
	}
	//sort(b,&b[(h-k+1)*2]);
	sort(b,&b[(h-k+1)]);
	sort(c,&c[h-k+1]);
	//cout<<b[0]<<endl;
	//for(int i=0;i<(h-k+1);i++){
		cout<<min(b[0],c[0])<<endl;
	//}
	return 0;
}