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 (1.42.0) (judge verdict: Accepted)

use std::io::*;
use std::str::FromStr;
use std::cmp;
use std::collections::HashMap;
use std::collections::HashSet;
use std::char;
use std::cmp::min;
use num_traits::abs;

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char) 
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

fn gcd(a: u64, b: u64) -> u64 {
    if b == 0 {
        a
    } else {
        gcd(b, a % b)
    }
}
fn read_tuple2<T: FromStr, S: FromStr>() -> (T, S) {
    let a = read();
    let b = read();
    (a, b)
}

fn count_two(n: u64) -> u64 {
    fn go(count:u64, num: u64) -> u64 {
        if num % 2 == 0 {
            go(count +1, num / 2)
        } else {
            count
        }
    }
    go(0, n)
}

fn main() {
    let (n, k): (usize, usize) = read_tuple2();
    let xs:Vec<i64> = (0..n).map(|_|read()).collect();
    let left_rights = (0_usize..n - k + 1).map(|s|(xs[s], xs[s + k - 1]));
    let calc_costs = |left, right| {
        let left_to_right = abs(left) + abs(right - left);
        let right_to_left = abs(right) + abs(left - right);
        min(left_to_right, right_to_left)
    };
    let ans = left_rights.map(|(left, right)|calc_costs(left, right)).min().unwrap();
    println!("{}", ans);

}