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>
#include <stdlib.h>
#define ABS(a) ((a < 0)? -a : a)
#define MIN(a, b) ((a < b)? a : b)

void solve(int *x, int n, int k) {
    int i, min = 1e9+7, tmp, tmp1, tmp2;
    for(i = 0; i < n-k+1; ++i) {
        tmp1 = ABS(x[i]) + ABS(x[k - 1 + i] - x[i]);
        tmp2 = ABS(x[k - 1 + i]) + ABS(x[k - 1 + i] - x[i]);
        tmp = MIN(tmp1, tmp2);
        min = MIN(tmp, min);
    }
    printf("%d\n", min);
}

int main(void)
{
    int N, K, i;
    scanf("%d %d", &N, &K);
    int *x = (int*)malloc((N+1)*sizeof(int));
    for(i = 0; i < N; ++i) { scanf("%d", &x[i]); }
    solve(x, N, K);
    return 0;
}