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)

import bisect
n, k = map(int, input().split())
X = list(map(int, input().split()))

ans = float('inf')

for i in range(n):
    # 左に走る
    if X[i] <= 0:
        if 0 <= i+k-1 < n-1:
            temp = 0
            temp+= -X[i]*2
            if X[i+k-1] >= 0:
                temp += X[i+k-1]
                ans = min(ans, temp)
        if 0 <= i-k+1 < n-1:
            ans = min(ans, -X[i-k+1])

    # 右に走る
    elif X[i] > 0:
        if 0 <= i-k+1 < n-1:
            temp = 0
            temp+=X[i]*2
            if X[i-k+1] <= 0:
                temp -= X[i-k+1]
                ans  = min(ans, temp)
        if 0 <= i+k-1 < n-1:
            ans = min(ans, X[i+k-1])

if n == 1:
    ans = abs(X[0])

print(ans)