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 JavaScript (node.js v5.12) (judge verdict: Accepted)

'use strict'

const main = (input) => {
    input = input.split('\n')
    const N = parseInt(input[0].split(' ')[0])
    const K = parseInt(input[0].split(' ')[1])
    const arr = input[1].split(' ').map(v => parseInt(v))

    let dist = 100000000000
    // 通るべき点を調べ上げる
    for(let i = 0; i <= arr.length - K; i++){
        let left = arr[i]
        let right = arr[i + K - 1]
        // 左端からスタートするときの距離
        const a = Math.abs(left) + Math.abs(left - right)
        // 右端からスタートするときの距離
        const b = Math.abs(right) + Math.abs(right - left)
        const min = Math.min(a, b)
        if(dist > min){
            dist = min
        }
    }
    console.log(dist)
}

main(require('fs').readFileSync('/dev/stdin', 'utf-8'))