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>
#include <math.h>

int minf(int i,int j){
  if(i<j){
    return i;
  }else{
    return j;
  }
}

int absf(int n){
  if(n>0){
    return n;
  }else{
    return -n;
  }
}

int main(){
  int i,N,K;
  scanf("%d" "%d",&N,&K);
  int X[N];
  for(i=0;i<N;i++){scanf("%d",&X[i]);}

  int cost1,cost2;
  int cost=X[N-1]+absf(2*X[0]);
  for(i=0;i<=N-K;i++){
    cost1=absf(X[i])+absf(X[i+K-1]-X[i]);
    cost2=absf(X[i+K-1])+absf(X[i+K-1]-X[i]);
    if(minf(cost1,cost2)<cost){
      cost=minf(cost1,cost2);
    }
  }
  printf("%d",cost);
  return 0;
}