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 (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"
)

////////////////////////////////////////
///        templates                 ///
////////////////////////////////////////

var sc = bufio.NewScanner(os.Stdin)

func nextLine() string {
	sc.Scan()
	return sc.Text()
}

var rdr = bufio.NewReaderSize(os.Stdin, 1000000)

func readBigLine() string {
	buf := make([]byte, 0, 1000000)
	for {
		l, p, e := rdr.ReadLine()
		if e != nil {
			panic(e)
		}
		buf = append(buf, l...)
		if !p {
			break
		}
	}
	return string(buf)
}

func strSprit(str string) []string {
	cols := strings.Split(str, " ")
	return cols
}

func parseInt(str string) int {
	n, _ := strconv.Atoi(str)
	return n
}

func intSprit(str string) []int {
	strs := strSprit(str)
	cols := make([]int, len(strs))
	for i, v := range strs {
		cols[i] = parseInt(v)
	}
	return cols
}

func bitCount(n uint) int {

	x := uint64(n)

	const m = 1<<64 - 1
	const m0 = 0x5555555555555555
	const m1 = 0x3333333333333333
	const m2 = 0x0f0f0f0f0f0f0f0f

	x = x>>1&(m0&m) + x&(m0&m)
	x = x>>2&(m1&m) + x&(m1&m)
	x = (x>>4 + x) & (m2 & m)
	x += x >> 8
	x += x >> 16
	x += x >> 32

	return int(x) & (1<<7 - 1)
}

func bitExist(n, i int) bool {
	return ((n >> uint(i)) & 1) == 1
}

func setBit(d, n int) int {
	t := 1 << uint(n)
	return d | t
}

func intAbs(n int) int {
	return int(math.Abs(float64(n)))
}

////////////////////////////////////////
///        end templates             ///
////////////////////////////////////////

func main() {
	line := readBigLine()
	spl := intSprit(line)

	N := spl[0]
	K := spl[1]

	x := intSprit(readBigLine())

	res := 1 << 30
	for i := 0; i < N-K+1; i++ {
		l := x[i]
		r := x[i+K-1]

		lr := intAbs(l) + intAbs(l-r)
		rl := intAbs(r) + intAbs(r-l)

		if res > lr {
			res = lr
		}
		if res > rl {
			res = rl
		}
	}
	fmt.Println(res)
}