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 proconio::input;
 
fn main() {
  input! {
    n: usize,
    mut k: usize,
    mut vals: [isize;n]
  }
  
  let mut min = isize::max_value();
  let mut index = n-1;
  loop {
    let i = index - k + 1;
    min = std::cmp::min(
      min,
      vals[index].abs() + (vals[index] - vals[i]).abs()
    );
    
    if i == 0 { break }
    index -= 1;
  }
  
  let mut index = 0;
  loop {
    let i = index + k-1;
    min = std::cmp::min(
      min,
      vals[index].abs() + (vals[index] - vals[i]).abs()
    );
    
    if n-1 <= i { break }
    index += 1;
  }
  println!("{}", min);
}