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>
using namespace std;

int main()
{
  int n,k;
  cin>>n>>k;
  vector<int> vec;
  for(int i=0;i<n;i++){
    int tmp;
    cin>>tmp;
    if(tmp==0) k--;
    else vec.push_back(tmp);
  }
  n=vec.size();
  if(k==0){
    cout<<0;
    return 0;
  }
  vector<int> ans;
  vector<int> tmp(k);
  for(int j=0;j<k;j++){
    tmp[j]=vec[j];
  }
  for(int i=k;i<=n;i++){   
    if(tmp[k-1]<0){
      ans.push_back(abs(tmp[0]));
    }
    else if(tmp[0]>0){
      ans.push_back(abs(tmp[k-1]));
    }
    else{
      if(abs(tmp[0])>tmp[k-1]){
        ans.push_back(abs(tmp[0])+2*tmp[k-1]);
      }
      else{
        ans.push_back(2*abs(tmp[0])+tmp[k-1]);
      }
    }
    tmp.erase(tmp.begin());
    tmp.push_back(vec[i]);
  }
  cout<<*min_element(ans.begin(),ans.end());
}