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)

num = input().split(" ")
zahyou = input().split(" ")
zahyou_int = []
num[0] = int(num[0])
num[1] = int(num[1])
for i in zahyou:
    zahyou_int.append(int(i))

rousoku = []
time = 4 * 10 ** 8
for i in range(num[0]-num[1]+1):
    if(i == 0 or (zahyou_int[i] <= 0 and zahyou_int[(i+num[1])] >= 0)):
        rousoku = zahyou_int[i:(i+num[1])]
        # print(rousoku)
        time_p = -min(0, min(rousoku)) * 2 + max(rousoku)
        time_m = max(0, max(rousoku)) * 2 - min(rousoku)
        if(min(time_p, time_m) < time):
            time = min(time_p, time_m)

print(time)