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: Accepted)

import sys
inputs = sys.stdin.readlines()
 
N, K = map(int, inputs[0].split())
X = list(map(int, inputs[1].split()))
 
if N == 1:
    print(X[0])
else:
    ans = 10 ** 9
    for i in range(N-K+1):
        x1, x2 = X[i], X[i+K-1]
        if x1 <= 0 and x2 <= 0:
            ans = min(ans, -x1)
        elif x1 <= 0 and 0 < x2:
            if -x1 < x2:
                ans = min(ans, -2*x1 + x2)
            else:
                ans = min(ans, -x1 + 2*x2)
        else:
            ans = min(ans, x2)
            break
    print(ans)