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 <math.h>

int time(int a, int b) {
	if ((long long int)a * b >= 0) return (abs(a) > abs(b)) ? abs(a) : abs(b);
	else return (2 * b - a > b - 2 * a) ? b - 2 * a : 2 * b - a;
}

int main() {
	int i, n, k, x[100010], r, l, t, min_t;
	scanf("%d%d", &n, &k);
	for (i = 0; i < n; i++) scanf("%d", &x[i]);
	for (i = 0; i + k - 1 < n; i++) {
		l = i; r = i + k - 1;
		t = time(x[l], x[r]);
		if (i == 0) min_t = t;
		if (min_t > t) min_t = t;
	}
	printf("%d", min_t);
	return 0;
}