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_usizepair() -> (usize, usize) {
    let mut input = String::new();
    let _ = std::io::stdin().read_line(&mut input);
    let v: Vec<usize> = input
        .trim()
        .split_whitespace()
        .map(|x| x.parse().unwrap())
        .collect();
    (v[0], v[1])
}

fn read_vec() -> Vec<i64> {
    let mut input = String::new();
    let _ = std::io::stdin().read_line(&mut input);
    input.trim().split_whitespace().map(|x| x.parse().unwrap()).collect()
}

fn main() {
    let (n, k) = read_usizepair();
    let x_list = read_vec();
    let mut cost: i64 = i64::max_value();

    for i in 0..(n - k + 1) {
        let low = i;
        let high = i + k - 1;
        if x_list[high].abs() < x_list[low].abs() {
            if x_list[high].abs() + x_list[high] - x_list[low] < cost {
                cost = x_list[high].abs() + x_list[high] - x_list[low];
            }
        } else {
            if x_list[low].abs() + x_list[high] - x_list[low] < cost {
                cost = x_list[low].abs() + x_list[high] - x_list[low];
            }
        }
    }

    println!("{}", cost);
}