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 min(int a,int b){
  if(a < b){
    return a;
  }
  return b;
}

int main(void){
  int N,K;
  scanf("%d%d",&N,&K);

  long long x[N];
  int start = -1;
  for(int i = 0;i < N;i++){
    scanf("%lld",&x[i]);
    if(x[i] > 0 && start == -1) start = i;
  }

  long long ans = 1e18;
  if(start+K-1 < N) ans = min(ans,x[start+K-1]);
  if(start-K >= 0) ans = min(ans,-x[start-K]);
  for(int i = 0;i < K && start+i < N;i++){
    if(start-(K-i+1) >= 0) ans = min(ans,2*x[start+i]-x[start-(K-i+1)]); 
  }
  for(int i = 1;i <= K && start-i >= 0;i++){
    if(start+(K-i-1) < N) ans = min(ans,-2*x[start-i]+x[start+(K-i-1)]);
  }

  printf("%d\n",ans);

  return 0;
}