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)

# coding: utf-8
# Your code here!
N,K=map(int,input().split())
X=list(map(int,input().split()))

def journey(main,sub):
    main=main[:]
    sub=list(map(lambda x:x*2,sub))
    
    ans=0
    for _ in range(K):
        if len(main)==0:
            ans+=sub.pop(-1)
        elif len(sub)==0:
            ans+=main.pop(-1)
        elif main[-1]<=sub[-1]:
            ans+=main.pop(-1)
        else:
            ans+=sub.pop(-1)
    
    return ans
    
i=0
while X[i]<0:
    i+=1

neg=[0]
pos=[0]
neg=neg+list(map(lambda x:x*(-1),X[:i][::-1]))
pos=pos+X[i:]
d_pos=[pos[i+1]-pos[i] for i in range(len(pos)-1)][::-1]#popしたいのでひっくり返す
d_neg=[neg[i+1]-neg[i] for i in range(len(neg)-1)][::-1]

a=(journey(d_pos,d_neg))
b=(journey(d_neg,d_pos))

print(min(a,b))