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

list($N, $K) = explode(" ", trim(fgets(STDIN)));
$cans = explode(" ", trim(fgets(STDIN)));

$min = 999999999;
$target_offset = $K - 1;
for ($i = 0; $i < count($cans) - $K + 1; $i++) {

    $min = get_min($min, $cans, $i, $target_offset);
}

$cans_rev = array_reverse($cans);
for ($i = 0; $i < count($cans_rev) - $K + 1; $i++) {

    $min = get_min($min, $cans_rev, $i, $target_offset);
}

print $min .PHP_EOL;

function get_min($min, $cans, $i, $target_offset)
{
    $offset = offset($cans, $i, $target_offset) + abs($cans[$i]);
    if($min > $offset)
    {
        $min = $offset;
    }
    return $min;
}

function offset($cans, $i, $target_end)
{
    if($cans[$i] < 0 && $cans[$i + $target_end] < 0)
    {
        return abs($cans[$i] - $cans[$i + $target_end]);
    }
    elseif ($cans[$i] < 0 && $cans[$i + $target_end] >= 0)
    {
        return abs($cans[$i]) + $cans[$i + $target_end];
    }
    else
    {
        return $cans[$i + $target_end] - $cans[$i]; 
    }
}