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: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;

int gcd(long long a, long long b){
  long long M = max(a, b), m = min(a, b);
  while(m != 0){
  	long long r = M%m;
    M = m; m = r;
  }
  return M;
}

int digit_sum(long long n){
  long long ans;
  while(n != 0){
  	ans += n%10;
  	n /= 10;
  }
  return ans;
}

int main(){
  int n, k;
  cin >> n >> k;
  vector<int> a(n);
  for(int i = 0; i < n; i++){
  	cin >> a.at(i);
  }
  int ans = 1000000000;
  
  for(int i = 0; i < n-k+1; i++){
    int dis = abs(a.at(i));
  	int wid = abs(a.at(i+k-1) - a.at(i));
  	ans = min(ans, dis + wid);
  }
  
  cout << ans << endl;
}