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 abs(int x){
    if (x>=0) return x;
    else      return -x;
}

int main(){
   int n,k,i,x[100000],m,mi,s,e,l;

   scanf("%d %d",&n,&k);
   for (i=0;i<n;i++) {
      scanf("%d",&x[i]);
      if (i==0) {
         m=x[0];mi=0;
      } else if (abs(x[i])<abs(m)) {
         m=x[i];mi=i;
      }
   }

   s=mi-k-1;
   if (s<0) s=0;
   e=mi+k;
   if (e>n) e=n+1;
   for (i=s;i<e-k;i++) {
      l=abs(x[i])+x[i+k-1]-x[i];
      if (i==s) m=l;
      else if (m>l) m=l;
   }
   printf("%d\n",m);
   return 0;
}