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>

int main()
{
  int n,k,x[100000];
  scanf("%d %d",&n,&k);
  int i;
  for(i=0;i<=n;i++)
  {
   scanf("%d",&x[i]);
  }
  
  int min,t,tmp;
  
  for(t=0;t+(k-1)<n;t++)
  {
	if(x[t]*x[t+(k-1)]>=0)
    {
      
      if(x[t]>=0)
      {
        tmp=x[t+k-1];
      }else{tmp=-x[t];}
      
    }else{
      
     if(-x[t]<x[t+k-1])
     {
       tmp=x[t+k-1]-2*x[t];
     }else{tmp=2*x[t+k-1]-x[t];}
     
    }
    if(t==0)
    {
      min=tmp;
    }else{
    
      if(min>tmp)
        min=tmp;
    }
  }
    
  printf("%d",min);
  return  0;
}