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)

from collections import deque

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

x_upper = []

for i in reversed(x):
    if i<0:
        break
    if i>=0:
        x_upper.append(i)
        x.pop()
        
#絶対値昇順へソート
x.reverse()
x_upper.reverse()

lenXu = len(x_upper)
lenX = len(x)

if K>lenXu:
    min = K-lenXu-1
    max = lenXu-1
else:
    min = -1
    max = K-1

S = []
while min<K and min<lenX:
    if min>=0:
        if (x[min]*(-1))<x_upper[max]:
            S.append((x[min]*(-1))*2 + x_upper[max])
        else:
            S.append((x[min]*(-1)) + x_upper[max]*2)
    else:
        S.append(x_upper[max])
    min += 1
    max -= 1

print(S_stock)