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)

use std::io::{BufRead, BufWriter, Write};

fn main() {
    let stdin = std::io::stdin();
    let stdout = std::io::stdout();
    solve(&mut stdin.lock(), &mut BufWriter::new(stdout.lock()));
}

fn solve<R: BufRead, W: Write>(stdin: &mut R, stdout: &mut BufWriter<W>) {
    let (n, k): (usize, usize) = stdin.gets().split(' ').values();
    let x = stdin.gets().split(' ').take(n).map(|x| x.parse().unwrap())
        .collect::<Vec<i32>>();
    let mut ans = std::i32::MAX;
    for pl in 0..n - k + 1 {
        let pr = pl + k - 1;
        let d = if x[pr] < 0 {
            -x[pl]
        } else if x[pl] < 0 {
            x[pr] - x[pl] + std::cmp::min(-x[pl], x[pr])
        } else {
            x[pr]
        };
        ans = std::cmp::min(ans, d);
    }
    writeln!(stdout, "{}", ans).unwrap();
}

trait Gets { fn gets(&mut self) -> String; }
impl<T: std::io::BufRead> Gets for T {
    fn gets(&mut self) -> String { self.lines().next().unwrap().unwrap() } }

trait Values<T> { fn values(&mut self) -> T; }
impl<'a, I, T1, T2> Values<(T1, T2)> for I
    where I: Iterator<Item=&'a str>,
          T1: std::str::FromStr, T1::Err: std::fmt::Debug,
          T2: std::str::FromStr, T2::Err: std::fmt::Debug {
    fn values(&mut self) -> (T1, T2) {
        (self.next().unwrap().parse().unwrap(),
         self.next().unwrap().parse().unwrap())
    }
}