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 Rust (1.15.1) (judge verdict: Accepted)

fn read<T: std::str::FromStr>() -> Vec<T> {
    let mut buf = String::new();
    std::io::stdin().read_line(&mut buf).ok();
    buf.split_whitespace()
        .map(|x| x.parse().ok().unwrap())
        .collect()
}

fn main() {
    let (n, k) = {
        let v: Vec<usize> = read();
        (v[0], v[1])
    };
    let x: Vec<i64> = read();

    let mut ans = 1_000_000_000;
    use std::cmp::{max, min};
    for i in 0..n - k + 1 {
        let tmp = if x[i] < 0 && x[i + k - 1] > 0 {
            x[i + k - 1] - x[i] + min(x[i + k - 1], -x[i])
        } else {
            max(x[i].abs(), x[i + k - 1].abs())
        };
        ans = min(ans, tmp);
    }
    println!("{}", ans);
}