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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;

class Main {
    public static void main(String... args) {        
        int N = IN.nextInt();
        int K = IN.nextInt();
        int[] x = new int[N];
        for (int i = 0; i < N; i++) {
            x[i] = IN.nextInt();
        }
        int ans = Integer.MAX_VALUE;
        int j;
        int dist;
        for (int i = 0; i <= N - K; i++) {
            j = i + K - 1;
            if (x[j] <= 0) {
                ans = Math.min(ans, -x[i]);
            } else if (0 <= x[i]) {
                ans = Math.min(ans, x[j]);
            } else {
                dist = Math.min(Math.abs(x[i]), x[j]);
                ans = Math.min(ans, x[j] - x[i] + dist);
            }
        }
        System.out.println(ans);
    }
    final static Scanner IN = new Scanner(System.in);
}