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)

#define _USE_MATH_DEFINES

#include <iostream>
#include <iomanip>
#include <stdio.h>

#include <sstream>
#include <algorithm>
#include <iterator>
#include <cmath>
#include <complex>

#include <string>
#include <cstring>
#include <vector>
#include <bitset>

#include <queue>
#include <set>
#include <map>
#include <stack>
#include <list>

#include <ctime>
////
//#include <random>//
/////////

typedef long long LL;
typedef long double LD;
typedef unsigned long long ULL;

////定数
const int INF = (int)1e9 + 10;
const LL MOD = (LL)1e9 + 7;
const LL LINF = (LL)4e18 + 20;
const LD PI = acos(-1.0);
const double EPS = 1e-9; 
/////////
using namespace::std;
template<typename T>
void chmax(T& a, T b) {
	a = max(a, b);
}

template<typename T>
void chmin(T& a, T b) {
	a = min(a, b);
}

template<typename T>
void IN(vector<T> &A,int N=-1) {
	if (N == -1) {
		N = A.size();
	}
	for (int i = 0; i < N; ++i) {
		cin >> A[i];
	}
}

template<typename T>
void SO(vector<T> &A,bool F=false) {
	sort(A.begin(), A.end());
	if (F) {
		reverse(A.begin(), A.end());
	}
}
//////////////
LL c2(LL a) {
	LL ans = a * (a - 1) / 2;
	return ans;
}
void solve() {
	int N,K;
	cin >> N >>K;
	vector<LL> X(N);
	IN(X);
	LL ans = LINF;
	for (int i = 0; i + K - 1 < N; ++i) {
		chmin(ans, (X[i + K - 1] - X[i]) + min(abs(X[i + K - 1]), abs(X[i])));
	}
	cout << ans << endl;
}

signed main(void) {
	std::cin.tie(0);
	std::ios::sync_with_stdio(false);
	std::cout << std::fixed;//小数を10進数表示
	cout << setprecision(16);//小数点以下の桁数を指定//coutとcerrで別	

	solve();
}