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>
#include <stdlib.h>

long long int cmpfunc (const void * a, const void * b)
{
   return ( *(long long int*)a - *(long long int*)b );
}

int main()
{
    long long  int n, k, i, j, sum = 0;
    scanf("%lld %lld", &n, &k);
    long long int ar[n+10], br[n-k+10];
    for (i=0; i<n; i++)
        scanf("%lld", &ar[i]);
    qsort(ar, n, sizeof(long long int), cmpfunc);
    for (i=0; i<=n-k; i++)
    {
        sum = abs(0 - ar[i]);
        for(j=i+1; j<=i+k-1; j++)
            sum = sum + (ar[j] - ar[j-1]);
        br[i] = sum;
        sum = 0;
    }
    qsort(br, n-k+1, sizeof(long long int), cmpfunc);

    printf("%lld", br[0]);
    return 0;
}