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, k, i;
  long long int x[100005], check, ans=-1;
  scanf("%d %d",&n, &k);
  for(i=0;i<n;i++) scanf("%lld",&x[i]);
  if(x[0]>=0) ans=x[k-1];
  else if(x[n-1]<=0) ans=abs(x[n-k]);
  else{
    for(i=0;i<n-k+1;i++){
      if(x[i+k-1]>=0){
        if(abs(x[i])<abs(x[i+k-1])) check=2*abs(x[i])+abs(x[i+k-1]);
        else check=abs(x[i])+2*abs(x[i+k-1]);
        if(check < ans || ans==-1) ans = check;
      }
    }
  }
  printf("%lld\n", ans);
  return 0;
}