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.io.*;

/**
 * Copyright © 2018 Chris. All rights reserved.
 *
 * @author Chris
 * 2018/6/23 11:55
 * @see meituan.n2018.Bturn
 */
public class Main {


    private static BufferedReader br;
    private static StreamTokenizer st;
    private static PrintWriter pw;


    private static void solve() throws IOException {
        int N = nextInt();
        int K = nextInt();

        int x[] = new int[N];
        int mid = 0;
        for (int i = 0; i < N; i++) {
            x[i] = nextInt();
            if (x[i] <= 0) {
                mid = i;
            }
        }

        int min = Integer.MAX_VALUE;
        for (int i = Math.max(0, mid - K + 1); i <= mid && (i + K - 1 < N); i++) {
            min = Math.min(min, Math.abs(x[i + K - 1] - x[i]) + Math.min(Math.abs(x[i + K - 1]), Math.abs(x[i])));
        }
        if (x[mid] < 0 && (mid + K) < N) {
            min = Math.min(min, x[mid + K]);
        }
        pw.print(min);
    }

    public static void main(String args[]) throws IOException {
//        boolean oj = System.getProperty("ONLINE_JUDGE") != null;
//        if (!oj) {
//            System.setIn(new FileInputStream("src/in.txt"));
//        }
        br = new BufferedReader(new InputStreamReader(System.in));
        st = new StreamTokenizer(br);
        pw = new PrintWriter(new OutputStreamWriter(System.out));
        st.ordinaryChar('\''); //指定单引号、双引号和注释符号是普通字符
        st.ordinaryChar('\"');
        st.ordinaryChar('/');

        long t = System.currentTimeMillis();
        solve();
//        if (!oj) {
//            pw.println("[" + (System.currentTimeMillis() - t) + "ms]");
//        }
        pw.flush();
    }


    private static int nextInt() throws IOException {
        st.nextToken();
        return (int) st.nval;
    }

    private static long nextLong() throws IOException {
        st.nextToken();
        return (long) st.nval;
    }

    private static double nextDouble() throws IOException {
        st.nextToken();
        return st.nval;
    }

    private static String[] nextSS(String reg) throws IOException {
        return br.readLine().split(reg);
    }

    private static String nextLine() throws IOException {
        return br.readLine();
    }
}