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: Accepted)

#include<stdio.h>

int main()
{
 int N;
 int K;
 long x[100005];
 long dist;
 long mindist=200000005;
 long distp;
 long distm;
 int i;

 scanf("%d %d",&N,&K);
 for(i=0;i<N;i++) scanf("%ld",&x[i]);
 mindist=2*(x[N-1]-x[0]);

 for(i=K-1;i<N;i++)
 {
  if(x[i]<0) dist=-x[i-K+1];
  if(x[i-K+1]>0) dist=x[i];
  if((x[i]>=0)&(x[i-K+1]<=0))
  {
   distp=2*x[i]-x[i-K+1];
   distm=x[i]-2*x[i-K+1];
   if(distp<distm)
   {
    dist=distp;
   }else{
    dist=distm;
   }
  }
  if(mindist>dist) mindist=dist;
 }
 printf("%ld\n",mindist);
 return 0;
}