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: Runtime Error)

#include <stdio.h>
#include <math.h>

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

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

long int cost(long int*X,int i,int K){
  return X[K+i-1]-X[i]+minf(X[K+i-1],-X[i]);
}


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

  i=0;
  while (X[i]<=0){i++;}
  k=i;

  long int cost1=X[N-1]-2*X[0];
  for(i=0;i<k;i++){
    if(X[K+i-1]>=0){
      if(cost(X,i,K)<cost1){
	cost1=cost(X,i,K);
      }
    }
  }

  long int cost2=X[N-1]-2*X[0];
  if(k+K-1<N){cost2=X[k+K-1];}

  long int cost3=X[N-1]-2*X[0];
  if(k-K>=0){cost3=-X[k-K];}

  long int cost4=minf(cost2,cost3);
  printf("%ld", minf(cost1,cost4));
  return 0;
}