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>
#include<iomanip>
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
typedef long long ll;
typedef long  l;
typedef pair<int,int> P;
const ll INF=1000000000000001;
const double PI=3.141592653589;


int main(){
  int n,k; cin>>n>>k;
  vector<int> x(n);
  rep(i,n) cin>>x[i];

  int ans=1000000009;
  int i=0;
  while(k+i-1<n){
    int l=x[i];
    int r=x[k-1+i];
    // cout<<"l "<<l<<" r "<<r<<endl;
    if(l<0){
      if(r<=0)
      ans=min(ans,-l);
      else{
        int g=min(-l*2+r,r*2-l);
        ans=min(ans,g);
      }
    }else{
      ans=min(ans,r);
    }
    i++;
    // cout<<"ans "<<ans<<endl;
  }
  cout<<ans<<endl;


  return 0;
}