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++ (Clang 10.0.0) (judge verdict: Accepted)

#include<cstdio>
#include<algorithm>
int n,k;
long long ans=1000000000,f[100005];
long long solve(int l,int r)
{
	if (f[l]>=0&&f[r]>=0) return f[r];
	else if (f[l]<=0&&f[r]<=0) return -f[l];
	else return f[r]-f[l]+std::min(f[r],-f[l]);
}
int main()
{
	scanf("%d%d",&n,&k);
	for (int i=1;i<=n;i++) scanf("%lld",&f[i]);
	for (int l=1;l<=n;l++)
	{
		int r=l+k-1;
		if (r>n) break;
		ans=std::min(ans,solve(l,r));
	}
	printf("%lld\n",ans);
	return 0;
}