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;
typedef long long ll;
typedef pair<int,int> pii;
#define pb push_back
#define mp make_pair
#define rep(i,n) for(int i=0;i<(n);++i)

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	int n,k;cin >> n >> k;
	vector<int> a;
	vector<int> b;
	rep(i,n){
		int x;
		cin >> x;
		if(x>=0) a.pb(x);
		else b.pb(-x);
	}
	reverse(b.begin(),b.end());
	int ans=1000000000,cnt=0,sum=0;
	rep(i,min((int)b.size(),k)){
		cnt=i+1;
		sum=b[i];
		if(cnt<k && a.size()>=k-cnt){
			sum+=b[i];
			sum+=a[k-cnt-1];
			cnt=k;
		}
		if(cnt==k) ans=min(ans,sum);
	}
	if(a.size()>=k) ans=min(ans,a[k-1]);
	if(b.size()==0) cout << a[k-1] << endl;
	else cout << ans << endl;
}