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 bisect

n,k=map(int,input().split())
x=list(map(int,input().split()))

zero_ind=bisect.bisect_left(x,0)
"""
print("max",0,k-zero_ind-1)
print("min",k,n-zero_ind)
print("max",1,k-n+zero_ind-1)
print("min",k,zero_ind+2)
"""
v,w=10**9,10**9
if(n-zero_ind >= k):v=abs(x[zero_ind+k-1])
if(zero_ind >= k):w=abs(x[zero_ind-k])

y=[10**9]
z=[10**9]

if(zero_ind != 0 and zero_ind != n):
    for i in range(max(0,k-zero_ind-1),min(k,n-zero_ind)):
        if(zero_ind+i<0 or zero_ind+i>=n or zero_ind-(k-i)+1<0 or zero_ind-(k-i)+1>=n):continue
        y.append(abs(x[zero_ind+i])+abs(x[zero_ind+i]-x[zero_ind-(k-i)+1]))
    for i in range(max(1,k-n+zero_ind-1),min(k,zero_ind+2)):
        if(zero_ind-i<0 or zero_ind-i>=n or zero_ind+(k-i)-1<0 or zero_ind+(k-i)-1>=n):continue
        z.append(abs(x[zero_ind-i])+abs(x[zero_ind-i]-x[zero_ind+(k-i)-1]))
    """
    y=[abs(x[zero_ind+i])+abs(x[zero_ind+i]-x[zero_ind-(k-i)+1]) for i in range(max(0,k-zero_ind-1),min(k,n-zero_ind))]
    z=[abs(x[zero_ind-i])+abs(x[zero_ind-i]-x[zero_ind+(k-i)-1]) for i in range(max(1,k-n+zero_ind-1),min(k,zero_ind+2))]
    """

"""
for i in range(k):
    print(abs(x[zero_ind+i]))
    print(x[zero_ind-(k-i)+1])

for i in range(1,k):
    print(abs(x[zero_ind-i]))
    print(x[zero_ind+(k-i)-1])
"""
print(min([v,w]+y+z))
"""
print(y)
print(z)
"""