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: Runtime Error)

package main

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

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

// Sort
type Val struct {
	id, num int
}
type ByNum []Val

func (a ByNum) Len() int           { return len(a) }
func (a ByNum) Less(i, j int) bool { return a[i].num < a[j].num }
func (a ByNum) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N, K := sc.nextInt(), sc.nextInt()
	minus := []int{}
	plus := []int{}
	for i := 0; i < N; i++ {
		x := sc.nextInt()
		if x < 0 {
			minus = append(minus, -x)
		} else {
			plus = append(plus, x)
		}
	}
	sort.Ints(minus)
	ans := []int{}
	if len(minus) >= K {
		ans = append(ans, minus[K-1])
	}
	if len(plus) >= K {
		ans = append(ans, plus[K-1])
	}
	count, i, j := 0, 0, 0
	plusList := []int{}
	minusList := []int{}
	for count < K {
		if i < len(plus) && (j >= len(minus) || plus[i] <= minus[j]) {
			plusList = append(plusList, plus[i])
			i++
		} else {
			minusList = append(minusList, minus[j])
			j++
		}
		count++
	}
	//fmt.Println(plusList, minusList)
	if len(minusList) == 0 || plusList[len(plusList)-1] < minusList[len(minusList)-1] {
		if len(minusList) == 0 {
			ans = append(ans, plusList[len(plusList)-1])
		} else {
			ans = append(ans, plusList[len(plusList)-1]*2+minusList[len(minusList)-1])
		}
	} else {
		if len(plusList) == 0 {
			ans = append(ans, minusList[len(minusList)-1])
		} else {
			ans = append(ans, minusList[len(minusList)-1]*2+plusList[len(plusList)-1])
		}
	}

	sort.Ints(ans)
	fmt.Fprintln(wtr, ans[0])
	wtr.Flush()
}