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)

N, K = map(int, input().split())
X    = list(map(int, input().split()))

X_pos = [x for x in X if x >= 0]
X_neg = [x for x in X if x <  0]

X_neg.reverse()

l_pos = len(X_pos)
l_neg = len(X_neg)

R = []

if l_neg == 0:
    R.append(X_pos[K-1])
elif l_pos == 0:
    R.append(-1 * X_neg[K-1])
else:
    for k in range(K):
        if k < l_pos and K-k-2 < l_neg:
            R.append(2 * X_pos[k] - X_neg[K-k-2])
        else:
            break
    for k in range(K):
        if k < l_neg and K-k-2 < l_pos:
            R.append(-2 * X_neg[k] + X_pos[K-k-2])
        else:
            break

print(min(R))