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)

#!/usr/bin/env python3
import sys
import itertools
import collections
from queue import Queue
import functools
import math
INF = 10**9


def solve(N: int, K: int, x: "List[int]"):
    x_neg = ([-xx for xx in x if xx < 0]+[0])[::-1]
    x_pos = [0] + [xx for xx in x if xx >= 0]

    # 左先を考える
    # print(x_neg)
    # print(x_pos)
    left = [x_neg[i]*2 + x_pos[K-i] for i in range(len(x_neg))
            if K-i < len(x_pos)]
    if len(left) > 0:
        ansleft = min(left)
    else:
        ansleft = INF

    # 右先
    right = [x_pos[i]*2 + x_neg[K-i] for i in range(len(x_pos))
             if K-i < len(x_neg)]
    if len(right) > 0:
        ansright = min(right)
    else:
        ansright = INF
    # print(left)
    # print(right)
    print(min(ansright, ansleft))

    return


def main():

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    K = int(next(tokens))  # type: int
    x = [int(next(tokens)) for _ in range(N)]  # type: "List[int]"
    solve(N, K, x)


if __name__ == '__main__':
    main()