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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>

#define rep(i, n) for(int (i) = 0; (i) < (n); (i)++)

using namespace std;

template <class T>
void printv(vector<T> v)
{
  cout << '[';
  for (auto vec: v)
  {
    cout << vec << ' ';
  }
  cout << ']' << endl;
}

int main()
{
  long long n, k;
  long long point = 0;
  cin >> n >> k;

  vector<pair<int, int>> v;
  vector<long long> result;

  rep(i, n)
  {
    int tmp, tmp2;
    cin >> tmp;

    tmp2 = tmp < 0 ? -1 : 1;
    if (tmp2 == -1) point++;

    v.push_back(make_pair(tmp, tmp2));
  }

  point--;
  rep(i, n - k + 1)
  {
    if (i + k - 1 == point)
    {
      result.push_back(abs(v[i].first));
    }
    else if (i == point + 1)
    {
      result.push_back(abs(v[i + k - 1].first));
    }
    else if ((i <= point && i + k -1 > point))
    {
      result.push_back(abs((v[i].first) * 2) + abs((v[i + k -1].first)));
      result.push_back(abs((v[i].first)) + abs((v[i + k -1].first) * 2));
    }
  }

  sort(result.begin(), result.end());
  cout << result[0] << endl;
}