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>

int main(void) {
    int n,k,x[100000],i,max,min,kari,ans = 999999999;
    scanf("%d %d",&n,&k);
    for (i = 0;i < n;i++) {
        scanf("%d",&x[i]);
    }
    for (i = 0;i < n - k + 1;i++) {
        min = x[i];
        max = x[i + k - 1];
        if (min >= 0) {
            kari = max;
        } else if (max <= 0) {
            kari = -min;
        } else {
            if (max >= min * -1) {
                kari = -min * 2 + max;
            } else {
                kari = max * 2 + -min;
            }
        }
        if (kari < ans) ans = kari;
    }
    printf("%d\n",ans);
    return 0;
}