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 Kotlin (1.0.0) (judge verdict: Wrong Answer)

import java.util.*

fun main(args: Array<String>) {
    val sc = Scanner(System.`in`)
    val n = sc.nextInt()
    val k = sc.nextInt()
    val x = (0 until n).map { sc.next().toLong() }
    println(problem107c(n, k, x))
}

fun problem107c(n: Int, k: Int, x: List<Long>): Long {
    var min = Long.MAX_VALUE
    for (i in 0 .. n - k) {
        if (i < 0 && x[i + 1] < 0) continue
        if (i > 0 && x[i - 1] > 0) continue
//        debugLog(i, x[i], x[i + k - 1], Math.abs(x[i] - x[i + k - 1]) * 2, Math.abs(x[i] * 2 - x[i + k - 1]))
        if (x[i] > 0) {
            min = Math.min(min, x[i + k - 1])
            continue
        }
        min = listOf(min, Math.abs(x[i] - x[i + k - 1]) * 2, Math.abs(x[i] * 2 - x[i + k - 1])).min()!!
    }
    return min
}