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 main() {
    let mut nk = String::new();
    std::io::stdin().read_line(&mut nk).unwrap();
    let nk: Vec<usize> = nk.trim().split_whitespace().flat_map(str::parse).collect();
    let n = nk[0];
    let k = nk[1];

    let mut x = String::new();
    std::io::stdin().read_line(&mut x).unwrap();
    let x: Vec<isize> = x.trim().split_whitespace().flat_map(str::parse).collect();

    println!("{}", (0..(n - k+1)).map(|s| {
        let start = x[s];
        let end = x[s + k - 1];
        if start >= 0 {
            end
        } else if end > 0 {
            let a = -start * 2 + end;
            let b = -start + end * 2;
            if a < b { a } else { b }
        } else {
            -start
        }
    }).min().unwrap());
}