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)

def find_center(arr):
    for i in range(len(arr)-1):
        if arr[i] < 0 <= arr[i+1]:
            return i+1
    return len(arr) + 1

def candles(N,K,arr):
    center = find_center(arr)
    left = list(map(abs,arr[center-1::-1]))
    right = arr[center:]
    # print("center: {}".format(center))
    # print("left: {}".format(left))
    # print("right: {}".format(right))

    min_dis = None
    for i in range(min(len(left),K),-1,-1):
        left_dis = left[i-1]
        right_dis = right[K-i-1]
        # print("index: {}".format(i))
        # print("left_dis: {}".format(left_dis))
        # print("right_dis: {}".format(right_dis))

        if len(left[0:i]) < K:
            dis = left_dis * 2 + right_dis if left_dis < right_dis else right_dis * 2 + left_dis
        elif len(left[0:i]) == K:
            dis = left_dis
        elif len(right[0:K-i]) == K:
            dis = right_dis
        else:
            print("ERROR")

        # print("distance: {}".format(dis))

        if min_dis is None or dis < min_dis:
            min_dis = dis

    return min_dis

    


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

print(candles(N,K,arr))