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: Wrong Answer)

package main

import (
	"bufio"
	"bytes"
	"fmt"
	"log"
	"os"
	"strconv"
)

// const abcd = "abcdefghijklmnopqrstuvwxyz"
// const ABCD = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
var dr = [...]int{0, 1, 1, 1, 0, -1, -1, -1, 0}
var dc = [...]int{1, 1, 0, -1, -1, -1, 0, 1, 0}

func main() {
	log.SetFlags(log.Lshortfile)
	nextReader = NewScanner()
	N := nextInt()
	K := nextInt()
	x := nextInts(N)
	start := 0
	for i := 0; i < N; i++ {
		if x[i] > 0 {
			break
		} else {
			start++
		}
	}
	start = min(N-1, start)
	ans := x[N-1] - x[0]
	for i := 0; i < N-K; i++ {
		j := i + K - 1
		if start == 0 {
			ans = min(ans, x[j])
		} else {
			len1 := 2*(-x[i]) + x[j]
			len2 := -x[i] + 2*x[j]
			ans = min(ans, len1, len2)
		}
	}
	fmt.Println(ans)
}

func max(a ...int) int {
	r := a[0]
	for i := 0; i < len(a); i++ {
		if r < a[i] {
			r = a[i]
		}
	}
	return r
}
func min(a ...int) int {
	r := a[0]
	for i := 0; i < len(a); i++ {
		if r > a[i] {
			r = a[i]
		}
	}
	return r
}
func sum(a []int) (r int) {
	for i := range a {
		r += a[i]
	}
	return r
}
func minmax(a, b int) (int, int) {
	if a > b {
		return b, a
	}
	return a, b
}

func abs(a int) int {
	if a < 0 {
		return -a
	}
	return a
}

func printInts(out []int, str string) {
	var bb bytes.Buffer
	for i := range out {
		bb.WriteString(strconv.Itoa(out[i]))
		bb.WriteString(str)
	}
	fmt.Println(bb.String())
}

var nextReader func() string

func NewScanner() func() string {
	r := bufio.NewScanner(os.Stdin)
	r.Buffer(make([]byte, 1024), int(1e+11))
	r.Split(bufio.ScanWords)
	return func() string {
		r.Scan()
		return r.Text()
	}
}
func nextString() string {
	return nextReader()
}
func nextInt64() int64 {
	v, _ := strconv.ParseInt(nextReader(), 10, 64)
	return v
}
func nextInt() int {
	v, _ := strconv.Atoi(nextReader())
	return v
}
func nextInts(n int) []int {
	r := make([]int, n)
	for i := 0; i < n; i++ {
		r[i] = nextInt()
	}
	return r
}
func nextFloat64() float64 {
	f, _ := strconv.ParseFloat(nextReader(), 64)
	return f
}