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)

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

m = []
p = []
for i in range(n):
    if x[i] < 0:
        m.append(x[i])
    elif x[i] > 0:
        p.append(x[i])

if m and p:
    if k-len(m) >= 0:
        s = 0
    else:
        s = abs(k-len(m))+1
    
    i = 0
    ans = float('inf')
    while s+i <= len(m) and z+s+i <= n:
        ans = min(ans, min(abs(x[s+i])*2 + abs(x[k-1+s+i]), abs(x[s+i]) + abs(x[k-1+s+i])*2))
        
        if s+i == len(m):
            ans = min(ans, x[k-1+s+i])
        if z+s+i == len(m)-1:
            ans = min(ans, abs(x[s+i]))
        i += 1
    
    print(ans)
elif m:
    print(abs(x[-k]))
elif p:
    print(x[k-1])
else:
    print(0)