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)

n, k = (int(i) for i in input().split())
x = [int(i) for i in input().split()]
if n == k:
    if x[0] >= 0: print(x[-1])
    elif x[0] < 0 and x[-1] < 0: print(abs(x[0]))
    else:
        if abs(x[0]) < x[-1]: print(abs(x[0]) * 2 + x[-1])
        else: print(abs(x[0]) + x[-1] * 2)
else:
    d = []
    for i in range(n-k):
        st = i
        e = i+k-1
        if x[st] >= 0:
            d.append(x[e])
        if x[st] < 0 and x[e] < 0:
            d.append(abs(x[st]))
        else:
            if abs(x[st]) <  x[e]: d.append(abs(x[st]) * 2 + x[e])
            else: d.append(abs(x[st]) + x[e] * 2)
    print(min(d))