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 PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php
fscanf(STDIN, "%d %d", $N, $K);
$x = explode(" ", trim(fgets(STDIN)));

$answer = PHP_INT_MAX;

for ($i = 0; $i < $N - $K + 1; $i++) {
	$tmp = 0;
	if ($x[$i] < 0) {
		$tmp -= $x[$i];
		$tmp += $x[$i + $K - 1] - $x[$i];
	} else {
		$tmp = $x[$i + $K - 1];
	}

	echo $tmp . " " . $tmp2 . PHP_EOL;
	$answer = min($answer, $tmp);

	// 0以上なら抜ける
	if ($x[$i] >= 0) {
		break;
	}
}
for ($i = $N - 1; $i >= $K - 1; $i--) {
	$tmp = 0;
	if ($x[$i] > 0) {
		$tmp -= $x[$i];
		$tmp += $x[$i] - $x[$i - $K + 1];
	} else {
		$tmp = $x[$i - $K + 1];
	}

	$answer = min($answer, $tmp);

	// 0以上なら抜ける
	if ($x[$i] <= 0) {
		break;
	}
}

echo $answer;