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 Ruby (2.3.3) (judge verdict: Accepted)

n, k = gets.split(" ").map(&:to_i)

l0 = []
m0 = []

gets.split(" ").each do |x|
  x = x.to_i
  if x < 0
    l0.unshift(-x)
  else
    m0 << x
  end
end

ans = 4 * 10**8 + 1
ans = [ans, m0[k - 1]].min if m0.length >= k
ans = [ans, l0[k - 1]].min if l0.length >= k

1.upto(k - 1) do |i|
  a = []
  
  if l0.length >= i && m0.length >= (k - i)
    a << l0[i - 1]*2 + m0[k - i - 1]
  end
 
  if m0.length >= i && l0.length >= (k - i)
    a << m0[i - 1]*2 + l0[k - i - 1]
  end
  
  ans = [a.min, ans].min if a.size > 0
end

puts ans