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;

#ifdef DEBUG_MODE
	#define DBG(n) n;
#else
	#define DBG(n) ;
#endif
#define REP(i,n) for(ll (i) = (0);(i) < (n);++i)
#define PB push_back
#define MP make_pair
#define FI first
#define SE second
#define SHOW1d(v,n) {for(int W = 0;W < (n);W++)cerr << v[W] << ' ';cerr << endl << endl;}
#define SHOW2d(v,i,j) {for(int aaa = 0;aaa < i;aaa++){for(int bbb = 0;bbb < j;bbb++)cerr << v[aaa][bbb] << ' ';cerr << endl;}cerr << endl;}
#define ALL(v) v.begin(),v.end()
#define Decimal fixed<<setprecision(20)
#define INF 1000000000
#define LLINF 1000000000000000000LL
#define MOD 1000000007

typedef long long ll;
typedef pair<ll,ll> P;

ll AA[111111];
ll BB[111111];

int main(){
	int n,k;
	cin >> n >> k;
	vector<ll> a;
	vector<ll> b;
	
	REP(i,n) {
		int tmp;cin >> tmp;
		if(tmp > 0)a.PB(tmp);
		else b.PB(-tmp);
	}
	
	sort(ALL(a));
	sort(ALL(b));
	
	REP(i,111110){
		AA[i+1] = LLINF;
		BB[i+1] = LLINF;
	}
	
	REP(i,a.size()){
		AA[i+1] = a[i]*2;
	}
	
	REP(i,b.size()){
		BB[i+1] = b[i]*2;
	}
	
	ll ans = LLINF;
	
	REP(i,a.size()){
		if(k-i-1 >= 0 && BB[k-i-1] != LLINF){
			ans = min(ans,a[i]+BB[k-i-1]);
		}
	}
		
	REP(i,b.size()){
		if(k-i-1 >= 0 && AA[k-i-1] != LLINF){
			ans = min(ans,b[i]+AA[k-i-1]);
		}
	}
	
	cout << ans << endl;
		
	
	return 0;
}