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 Python (3.4.3) (judge verdict: Runtime Error)

import sys

n, k = map(int, input().split())
p = list(map(int, input().split()))

for i, n in enumerate(p):
  if n >= 0:
    zero_i = i
    break
    
n_list = p[:zero_i]
p_list = p[zero_i:]

if len(n_list) >= k:
  n_list = n_list[-k:]

if len(p_list) >= k:
  p_list = p_list[:(k+1)]
  
if len(n_list) == 0:
  print(p_list[k-1])
  sys.exit()
elif len(p_list) == 0:
  print(abs(n_list[-k]))
  sys.exit()
  
# e.g. n_list = [-30,-10]
if len(n_list) == k:
  min_move = abs(n_list[0])
else:
    n_min = abs(n_list[0]) + (p_list[k-len(n_list)]*2) 
    p_min = (abs(n_list[0])*2) + p_list[k-len(n_list)]
    min_move = min(n_min, p_min)

for i, n in enumerate(n_list):
  if (k-(i+1)) > len(p_list):
    break

  if i == len(n_list)-1:
    min_move = min(min_move, p_list[-1])
  else:
    n_min = abs(n_list[i+1]) + (p_list[i+1]*2) 
    p_min = (abs(n_list[i+1])*2) + p_list[i+1]
    min_move = min(min_move, n_min, p_min)
    
print(min_move)