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)

import sys

def ans(index, array, k):
    r = right(index, array, k)
    l =  left(index, array, k)
    return min(r, l)


def right(index, array, k):
    start = max(0, k-(index-1)) + index
    count = sys.maxsize
    for i in range(start, min(len(array), k+index+1)):
        tmp = array[i]
        tmp += array[i] - array[k -(i - index + 1)]
        count = count if count < tmp else tmp

    if n > (index + k - 1):
        count = count if count < array[index + k - 1] else array[index + k - 1]
    
    return count

def left(index, array, k):
    n = len(array)
    start = min(0, n-index-k) + index
    count = sys.maxsize
    
    for i in range(max(0, start - k), start):
        tmp = -array[i]
        tmp += -array[i] + array[k + i - 1]
        count = count if count < tmp else tmp

    if index >= k:
        count = count if count < -array[index-k] else -array[index-k]
    
    return count

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

x = [int(i) for i in input().split()] 

for i in range(n):
    if x[i] >= 0:
        index = i
        break

print(ans(index, x, k))