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: Time Limit Exceeded)

N,K = map(int,input().split())
ary = [0]+list(map(int,input().split()))
dp = [[0]*(N+1) for _ in range(N+1)]
ary = sorted(ary)
a = ary.index(0)
ans = float("Inf")
for i in range(N+1):
    for j in range(N+1):
        dp[i][j] = abs(ary[i]-ary[j])
for i in range(N+1):
        if i == a:continue
        k = abs(i - a)
        d = abs(ary[i])
        if k >= K and ans > d:
            ans = d
        if i <= a:
            k = K - abs(i-a)
            d = abs(ary[i])
            if k > 0:
                d += dp[i][a+k]
                if ans > d:
                    ans = d
print(0 if ans == float("Inf") else ans)