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: Accepted)

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

l = []
r = []
for i in range(n):
  x = xs[i]
  if x < 0:
    l.append(x)
  else:
    r.append(x)
    
if l == []:
  print(r[k-1])
  exit()
elif r == []:
  print(-l[-k])
  exit()
  
if n == k:
  print(min(r[-1], -l[0])*2+max(r[-1], -l[0]))
  exit()
  
ts = []
for i in range(max(k-len(l), 0), min(len(r), k+1)):
  if i == 0:
    t = -l[-k]
  elif i == k:
    t = r[k-1]
  else:
    t = min(r[i-1], -l[-(k-i)])*2+max(r[i-1], -l[-(k-i)])
  ts.append(t)
#print(ts)
print(min(ts))