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++ (GCC 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
#define PI 3.14159265359
#define NIL (-1)
#define LL long long
using namespace std;
const int64_t MOD = 1e9 + 7;
const int INF = INT_MAX;

int main() {
	int N, K;
	cin >> N >> K;

	vector<int> v(N);
	for (int i = 0; i < N; i++) {
		cin >> v.at(i);
	}

	int ans = INT_MAX;
	for (int i = 0; i < N - K + 1; i++) {
		int L, R;
		L = v.at(i);
		R = v.at(i + K - 1);

		int dist = 0;
		if ((L < 0) && (R > 0)) {
			dist = min(abs(L), abs(R)) * 2 + max(abs(L), abs(R));
		}
		else {
			if (R < 0) dist = abs(L);
			else dist = abs(R);
		}

		ans = min(ans, dist);
	}

	cout << ans << endl;
}