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: Wrong Answer)

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

inf = 10**18
l = inf
r = inf
n.times{|i|
  l = i if x[i]<0
  k-=1 if x[i]==0
  if x[i]>0
    r = i
    break
  end
}

a = [inf]*n
b = [inf]*n

if l!=inf
  (l+1).times{|i|
    a[i] = -x[l-i]
  }
end

if r!=inf
  (n-r).times{|i|
    b[i] = x[r+i]
  }
end

if k==0
  p 0
  exit
end

min = inf
(l+1).size.times{|i|
  if i<k-1
    tmp = a[i]*2 + b[k-i-2]
    min = tmp if min > tmp
  else
    tmp = a[i]
    min = tmp if min > tmp
    break
  end
}
(n-r).size.times{|i|
  if i<k-1
    tmp = b[i]*2 + a[k-i-2]
    min = tmp if min > tmp
  else
    tmp = b[i]
    min = tmp if min > tmp
    break
  end
}

p min