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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
class Program{
  public static int min(int x, int y){
    if (x >= y){
      return y;
    }
    else{
      return x;
    }
  }
  public static void Main(){
    int N, K;
    var NKL = Console.ReadLine().Split(' ');
    N = int.Parse(NKL[0]);
    K = int.Parse(NKL[1]);
    var A = new int[N];
    var line = Console.ReadLine().Split(' ');
    for (int i=0;i<N;i++){
      A[i] = int.Parse(line[i]);
    }
    int M = 2147483646;
    for (int k=0;k<N-K+1;k++){
      if (A[k] < 0 && A[k+K-1] > 0){
        int s = min(A[k+K-1] - 2 * A[k], 2 * A[k+K-1] - A[k]);
        M = min(s, M);
      }
      else if (A[k] <= 0 && A[k+K-1] <= 0){
        M = min(-A[k], M);
      }
      else if (A[k] >= 0 && A[k+K-1] >= 0){
        M = min(A[k+K-1], M);
      }
    }
    Console.WriteLine(M);
  }
}