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 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;
int main()
  {int N, K; cin >> N >> K;
  vector<int> xs(N); for (auto &x : xs) cin >> x;
  int ans = 1e9;
  for (int j = N - 1; j >= 0 and xs[j] >= 0; --j)
    {auto i = j - K + 1;
    if (i >= 0) ans = min(ans, (xs[i] < 0) * 2 * abs(xs[i]) + xs[j]);}
  for (int j = 0; j < N and xs[j] <= 0; ++j)
    {auto i = j + K - 1;
    if (i < N) ans = min(ans, (xs[i] > 0) * 2 * xs[i] + abs(xs[j]));}
  cout << ans << endl;}