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)

// by syu
package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"sort"
	"strconv"
)

var in = NewScanner(os.Stdin, 16777216)

func main() {
	N, K := in.Int(), in.Int()
	x := in.ArrayInt(N)
	sort.Ints(x)
	min := 999999999
	for i := 0; i < N-K+1; i++ {
		sum := Abs(x[i])
		for j := 0; j < K-1; j++ {
			sum += x[i+j+1] - x[i+j]
		}
		if sum < min {
			min = sum
		}
	}
	Pln(min)
}

type Scanner struct {
	*bufio.Scanner
}

func NewScanner(r io.Reader, max int) *Scanner {
	s := bufio.NewScanner(r)
	s.Split(scanWords)
	if max <= 0 {
		max = 1048576
	}
	s.Buffer([]byte{}, max)
	return &Scanner{s}
}
func (s *Scanner) Int() int {
	s.Scan()
	i, e := strconv.ParseInt(s.Text(), 10, 64)
	if e != nil {
		panic(e)
	}
	return int(i)
}
func (s *Scanner) ArrayInt(n int) (r []int) {
	for i := 0; i < n; i++ {
		r = append(r, s.Int())
	}
	return
}
func isSpace(b byte) bool {
	return b == ' ' || b == '\n' || b == '\r' || b == '\t'
}
func scanWords(data []byte, atEOF bool) (advance int, token []byte, err error) {
	start := 0
	for start < len(data) && isSpace(data[start]) {
		start++
	}
	for i := start; i < len(data); i++ {
		if isSpace(data[i]) {
			return i + 1, data[start:i], nil
		}
	}
	if atEOF && len(data) > start {
		return len(data), data[start:], nil
	}
	return start, nil, nil
}
func Abs(n int) int {
	y := n >> 63
	return (n ^ y) - y
}
func Pln(s ...interface{}) {
	fmt.Println(s...)
}