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)

io = STDIN
n,$k=io.gets.split.map(&:to_i)
ar = io.gets.split.map(&:to_i)
plus =ar.select{|x|x>=0}
minus =ar.select{|x|x<0}.map{|x|-x}.reverse
def calc2(pct,mct,plus,minus)
  min=[plus[pct-1],minus[mct-1]].min
  max=[plus[pct-1],minus[mct-1]].max
  min*2 + max
end
def calc(ar,plus,minus)
  ans=Float::INFINITY
  (0..plus.size).each do |pct|
    mct=$k-pct
    if mct <= minus.size
      ans=[ans,calc2(pct,mct,plus,minus)].min
    end
  end
  ans
end
if plus ==[]
  puts minus[$k-1]
elsif minus ==[]
  puts plus[$k-1]
else
  puts calc(ar,plus,minus)
end