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)

n,k = map(int,input().split())
# n,k = map(int,"8 5".split())
xn = list(map(int,input().split()))
# xn = list(map(int,"-9 -7 -4 -3 1 2 3 4".split()))

ans = float("inf")
for i in range(n-k+1):
#     print(xn[i],xn[n-k+i])
#     print(xn[i:i+k])
    tmp = min(abs(xn[i]),abs(xn[k+i-1])) + xn[k+i-1] - xn[i]
#     print("始点 is {}, 終わり is {}, 始まり is {}".format(min(abs(xn[i]),abs(xn[k+i-1])), xn[k+i-1],xn[i]))
#     print("tmp is {}".format(tmp))
    if tmp < ans:
        ans=tmp
print(ans)