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: Wrong Answer)

#include<bits/stdc++.h>
using namespace std ;

int main()
{
	int n, k ;
	cin >> n >> k ;

	if(k==0)
	{
		cout << 0 ;
		return 0 ;
	}

	int a[n] ;

	for(int i=0;i<n;i++)
	{
		cin >> a[i] ;
	}

	int x=0 ;

	if(a[0]>=0)
	{
		cout << a[k-1] ;
		return 0 ;
	}

	if(a[n-1]<=0)
	{
		cout << a[n-k] ;
		return 0 ;
	}

	for(int i=1;i<n;i++)
	{
		if((a[i]>0)&&(a[i-1]<=0))
		{
			x=i ;
			break ;
		}
	}

	int ans=INT_MAX ;

	for(int i=1;i<=k;i++)
	{
		if(((x+i-1)>=n)||((x-k+i)<0))
		{
			continue ;
		}

		int sol=min(((2*a[x+i-1])+abs(a[x-k+i])),((abs(2*a[x-k+i]))+a[x+i-1])) ;

		if(sol<ans)
		{
			ans=sol ;
		}
	}

	cout << ans ;

	return 0 ;
}