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)

# -*- coding: utf-8 -*-
from bisect import bisect, bisect_left
def inpl(): return list(map(int, input().split()))
N, K = inpl()
X = inpl()
ans = 10**9

r0 = bisect_left(X, 0)

for i in range(N):
    #print(r0+i, r0-K+i+1)
    if (0 <= r0+i < N) and (0 <= r0-K+i+1 < N):
        if X[r0+i] < 0 or X[r0-K+i+1] > 0:
            continue
        #print(2*X[r0+i] - X[r0-K+i+1])
        #print(X[r0+i] - 2*X[r0-K+i+1])
        ans = min(ans, 2*X[r0+i] - X[r0-K+i+1])
        ans = min(ans, X[r0+i] - 2*X[r0-K+i+1])

if r0+K-1 < N:
    ans = min(X[r0+K-1], ans)
if r0-K >= 0:
    ans = min(-X[r0-K], ans)

print(ans)