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<map>
#include<iostream>
#include<deque>
#include<algorithm>
#include<string>
#include<cctype>
#include<iomanip>
#include<vector>
#include<queue>
 
using namespace std;
#define REP(i,b,e) for(ll i=(ll)b;i<(ll)e;i++)
#define rep0(i,n) REP(i,0ll,n)
#define rep1(i,n) REP(i,1ll,n+1)
 
#define shosu setprecision(10)
 
typedef long long ll;
typedef pair<int,int> P;
ll longinf=1ll<<60;
int inf=1<<29;

ll N;
ll K;
ll x[100002];
ll s[100002];



int main(){
      cin>>N>>K;
      rep0(i,N) cin>>x[i];
      ll ans=longinf;
      rep0(i,N-K+1){
            s[i]=x[i+K-1]-x[i];
      }
      rep0(i,N-K+1){
            ans=min(ans,s[i] + min(abs(x[i+K-1]),abs(x[i]))); 
      }
      cout<<ans<<endl;

      return 0;
}