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


def solve(n, k, xxx):
    i0 = bisect.bisect(xxx, 0)
    if i0 == 0:
        return xxx[0]
    if i0 == n:
        return -xxx[-1]

    xxx.insert(i0, 0)
    # print(xxx)
    ans = float('inf')
    for p in range(k + 1):
        li = i0 - k + p
        ri = i0 + p
        # print(p, li, ri, -xxx[li] * 2 + xxx[ri], -xxx[li] + xxx[ri] * 2)
        if li < 0 or ri >= n:
            continue
        ans = min(ans, -xxx[li] * 2 + xxx[ri], -xxx[li] + xxx[ri] * 2)
    return ans


n, k = map(int, input().split())
xxx = list(map(int, input().split()))
print(solve(n, k, xxx))