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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"fmt"
	"math"
)

func main() {
	var n, k int
	fmt.Scan(&n, &k)
	positions, distances := make([]int, n), make([]int, n)
	for i := 0; i < n; i++ {
		fmt.Scan(&positions[i])
		if i > 0 {
			distances[i] = abs(positions[i] - positions[i - 1]) + distances[i - 1]
		}
	}
	min := math.MaxInt32
	for i := 0; i < n - k + 1; i++ {
		tmp := distances[i + k - 1] - distances[i] + min1(abs(positions[i]), abs(positions[i + k - 1]))
		if tmp < min {
			min = tmp
		}
	}
	fmt.Println(min)
}

func abs(x int) int {
	if x < 0 {
		return -1 * x
	} else {
		return x
	}
}

func min1(x, y int) int {
	if x < y {
		return x
	} else {
		return y
	}
}