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)

//　高速 EOF要
//macro_rules! input {(source = $s:expr, $($r:tt)*) => {let mut iter = $s.split_whitespace();input_inner!{iter, $($r)*}};($($r:tt)*) => {let mut s = {use std::io::Read;let mut s = String::new();std::io::stdin().read_to_string(&mut s).unwrap();s};let mut iter = s.split_whitespace();input_inner!{iter, $($r)*}};}
//macro_rules! input_inner {($iter:expr) => {};($iter:expr, ) => {};($iter:expr, $var:ident : $t:tt $($r:tt)*) => {let $var = read_value!($iter, $t);input_inner!{$iter $($r)*}};}
//macro_rules! read_value {($iter:expr, ( $($t:tt),* )) => {( $(read_value!($iter, $t)),* )};($iter:expr, [ $t:tt ; $len:expr ]) => {(0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()};($iter:expr, chars) => {read_value!($iter, String).chars().collect::<Vec<char>>()};($iter:expr, usize1) => {read_value!($iter, usize) - 1};($iter:expr, $t:ty) => {$iter.next().unwrap().parse::<$t>().expect("Parse error")};}
// 低速 EOF不要
macro_rules! input {(source = $s:expr, $($r:tt)*) => {let mut iter = $s.split_whitespace();let mut next = || { iter.next().unwrap() };input_inner!{next, $($r)*}};($($r:tt)*) => {let stdin = std::io::stdin();let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));let mut next = move || -> String{bytes.by_ref().map(|r|r.unwrap() as char).skip_while(|c|c.is_whitespace()).take_while(|c|!c.is_whitespace()).collect()};input_inner!{next, $($r)*}};}
macro_rules! input_inner {($next:expr) => {};($next:expr, ) => {};($next:expr, $var:ident : $t:tt $($r:tt)*) => {let $var = read_value!($next, $t);input_inner!{$next $($r)*}};}
macro_rules! read_value {($next:expr, ( $($t:tt),* )) => {( $(read_value!($next, $t)),* )};($next:expr, [ $t:tt ; $len:expr ]) => {(0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()};($next:expr, chars) => {read_value!($next, String).chars().collect::<Vec<char>>()};($next:expr, usize1) => {read_value!($next, usize) - 1};($next:expr, $t:ty) => {$next().parse::<$t>().expect("Parse error")};}

// https://beta.atcoder.jp/contests/arc101/tasks/arc101_a

fn main(){
    input!{N:i64,K:i64,x:[i64;N]};
//    let N:i64 = N;
//    let K:i64 = K;
//    let x:Vec<i64> = x;
    let windows = x.windows(K as usize);
    let mut ans = i64::max_value();
    for window in windows{
        let L = window.first().unwrap();
        let R = window.last().unwrap();
        if L*R < 0 {
            ans = std::cmp::min(ans,std::cmp::min(L.abs(),R.abs()) + L.abs() + R.abs());
        }else{
            ans = std::cmp::min(ans,std::cmp::max(L.abs(),R.abs()));
        }
    }
    println!("{}",ans);
}