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: Wrong Answer)

use std::io::stdin;
fn get_string() -> String {
    let mut s = String::new();
    stdin().read_line(&mut s).unwrap();
    s.trim().to_string()
}

macro_rules! input {
    ($single:ty) => ( get_string().parse::<$single>().unwrap() );
    ($plural:ty,) => ({
        let line = get_string();
        line.split_whitespace().map(|v| v.parse::<$plural>().unwrap()).collect::<Vec<$plural>>()
    });
    ($($plural:ty),+) => ({
        let line = get_string();
        let mut iter = line.split_whitespace();
        ($(iter.next().unwrap().parse::<$plural>().unwrap()),+)
    });
    ($single:ty; $times:expr) => ( (0..$times).map(|_| input!($single)).collect::<Vec<$single>>() );
    ($($plural:ty),+; $times:expr) => ( (0..$times).map(|_| input!($($plural),+)).collect::<Vec<($($plural),+)>>() );
}

#[allow(dead_code)]
fn get_value<T: std::str::FromStr>() -> T {
    get_string().parse().ok().unwrap()
}
#[allow(dead_code)]
fn get_values_for<T: std::str::FromStr>(times: u64) -> Vec<T> {
    (0..times).map(|_| get_value()).collect()
}
#[allow(dead_code)]
fn get_vector<T: std::str::FromStr>() -> Vec<T> {
    get_string()
        .split_whitespace()
        .map(|v| v.parse().ok().unwrap())
        .collect()
}
#[allow(dead_code)]
fn get_vectors_for<T: std::str::FromStr>(times: u64) -> Vec<Vec<T>> {
    (0..times).map(|_| get_vector()).collect()
}

fn main() {
    let (n, k) = input!(usize, usize);
    let x = input!(i64,);

    let z = x
        .iter()
        .enumerate()
        .skip_while(|v| v.1.is_negative())
        .next();
    let z = match z {
        Some(x) => x.0,
        None => n - 1,
    };

    let mut l;
    if z <= k {
        l = 0;
    } else {
        l = z - k;
    }

    let mut time = Vec::new();
    let x: Vec<_> = x.iter().map(|v| v.abs()).collect();
    let (lx, rx) = x.split_at(z);
    let mut lx = lx.to_vec();
    let mut rx = rx.to_vec();
    lx.push(0);
    rx.insert(0, 0);
    while l + k <= n && l <= z {
        let r = l + k - z;
        let l_score = lx[l];
        let r_score = rx[r];
        if l < r {
            time.push(2 * l_score + r_score);
        } else {
            time.push(l_score + 2 * r_score);
        }
        l += 1;
    }
    println!("{}", time.iter().min().unwrap());
}