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"
)

// 2018-08-25T20:07:28+0800
// 2018-08-25T20:14:21+0800
// 2018-08-25T20:37:15+0800
func main() {
	var N, K int
	fmt.Scanf("%d%d", &N, &K)
	x := make([]int, N)
	for i := 0; i < N; i++ {
		fmt.Scanf("%d", &x[i])
	}
	if K == 1 {
		//
	}
	out := math.MaxInt64
	var r, t int
	for i := 0; i < N; i++ {
		r = i + K - 1
		if r >= N {
			break
		}
		if (r+1 < N && x[r+1] < 0) || (i-1 >= 0 && x[i-1] > 0) {
			continue
		}
		if x[r] < 0 {
			t = -x[i]
			if t < out {
				out = t
			}
		} else if x[i] > 0 {
			t = x[r]
			if t < out {
				out = t
			}
		} else {
			t = x[r] - x[i] + x[r]
			if t < out {
				out = t
			}
			t = x[r] - x[i] - x[i]
			if t < out {
				out = t
			}
		}
	}

	fmt.Println(out)
}