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: Wrong Answer)

def run(n, k, x):
    ri = 0
    li = k-1
    if len(x) == 1:
        return x[0]
    x2 = x
    x = list(map(abs, x))
    for i in range(k, len(x)):
        if x[ri] > x[i]:
            ri = i-k+1
            li = i
        elif x[ri] == x[i]:
            if x[ri+1] > x[i-1]:
                ri = i-k+1
                li = i
        else:
            if x2[li] <= 0:
                return x[ri]
            elif x2[ri] >= 0:
                return x[li]
            elif x[ri] > x[li]:
                return x[ri] + 2*x[li]
            else:
                return 2*x[ri] + x[li]
    if x2[li] <= 0:
        return x[ri]
    elif x2[ri] >= 0:
        return x[li]
    elif x[ri] > x[li]:
        return x[ri] + 2*x[li]
    else:
        return 2*x[ri] + x[li]


def read_line():
    n, k = map(int, input().split())
    x = list(map(int, input().split()))
    return (n, k, x)


def main():
    n, k, x = read_line()
    print(run(n, k, x))


if __name__ == '__main__':
    main()