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 9.2.1) (judge verdict: Wrong Answer)

#include<stdio.h>

long long abs(long long a){
  if(a >= 0){
    return a;
  }
  else{
    return -a;
  }
}

int main(void){
  int n , k;
  scanf("%d %d",&n ,&k);

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

  int start , end;
  long long time , min = 1000000000000;
  for(int i = 0;i < n - k + 1;i ++){
    start = i;
    end = i + k - 1;
    if(i < zero && zero <= i + k ){
      time =  - x[start] + x[end];
      if(abs(x[start]) < abs(x[end])){
        time += abs(x[start]);
      }
      else{
        time += abs(x[end]);
      }
    }
    else if(i < zero){
      time = abs(x[start]);
    }
    
    else if(i >= zero){
      time = abs(x[end]);
    }
    //printf("%lld\n",time);
    if(min > time){
      min = time;
    }
  }

  printf("%lld\n",min);

  return 0;
}