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: Runtime Error)

#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<cmath>

using namespace std;

int main() {
	int n, k;
	int m, i, j, start, time, min_time = -1;
	vector<int>x;

	cin >> n >> k;

	for (i = 0; i < n; i++) {
		cin >> m;
		x.push_back(m);
	}

	for (i = 0; i < n; i++) {
		if (x[i] >= 0) {
			break;
		}
	}
	start = i;

	for (i = start - k; i <= start; i++) {
		if (i < 0)
			i = 0;
		if (i + k > n)
			break;
		time = abs(x[i]);
		for (j = 1; j < k ; j++) {
			time += abs(x[i + j] - x[i + j - 1]);
		}
		if (min_time > time || min_time == -1)
			min_time = time;
	}
	for (i = start + k - 1; i >= start - 1; i--) {
		if (i >= n)
			i = n - 1;
		if (i < 0)
			break;
		time = abs(x[i]);
		for (j = 1; j < k; j++) {
			time += abs(x[i - j] - x[i - j + 1]);
		}
		if (min_time > time)
			min_time = time;
	}

	cout << min_time;

	return 0;
}