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)

# cook your dish here
import bisect 
n,k = map(int,input().split())
x = list(map(int,input().split()))

w  = x.count(0)
for i in range(w):
    x.remove(0)

if k <= w:
    print(0)
else:
    k = k -w
    #print(x)

    r = bisect.bisect_left(x,0)
    
    if x[-1]<0:
        print(abs(x[len(x)-k]))
    elif x[0] > 0:
        print(x[k-1])    
    else:
        ass = 10 ** 10
        ans = 10**10
        for i in range(r,min(len(x),r + k )):
            if i-r+1 >= k:
                ans = abs(x[i])
            
            else:
                if i - k + 1 >= 0:
                    ans = x[i] + abs(x[i-k+1]) + min(x[i],abs(x[i-k+1]))
            ass = min(ass,ans)
        if r-k >= 0:
            ans = abs(x[r-k])
        ass = min(ass,ans)
        print(ass)