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++ (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#define rep(i,q) for(int i = 0; q > i; i++)
using namespace std;
int abbs(int way){
  if(way < 0){
    way *= -1;
  }
  return way;
}
int main(void){
  int max = 0;
  int N,K;
  cin >> N >> K;
  int x[N];
  rep(i,N) cin >> x[i];
  rep(i,N-K + 1){
    int tmp = 0;
    if(abbs(x[K + i - 1]) > abbs(x[i])){
      tmp += abbs(x[i]);
    } else {
      tmp += abbs(x[K + i - 1]);
    }
    tmp += x[K + i - 1] - x[i];
    if(i == 0 || max > tmp){
      max = tmp;
    }
  }
  cout << max << endl;
  return 0;
}