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 min(int x, int y) {
    if (x>=y) return y;
    else return x;
}

int abs0(int x) {
    if (x>=0) return x;
    else return -x;
}

int main(void){
    int N, K, a[100005], i, x, m;
    scanf("%d%d", &N, &K);
    for (i=1; i<=N; i++) scanf("%d", &a[i]);
    for (i=1; i<=N-K+1; i++) {
        if (a[i]>=0) x=a[i+K-1];
        else if (a[i+K-1]<=0) x=-a[i];
        else x=abs0(a[i])+abs0(a[i+K-1])+min(abs0(a[i]), abs0(a[i+K-1]));
        if (x<m || i==1) m=x;
    }
    printf("%d", m);
    return 0;
}