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;

int main() {

	ll n, k; cin >> n >> k;

	vector<ll> x(n);
	for (int i = 0; i < n; i++) cin >> x[i];

	ll ans;
	if (0 <= x[0]) {
		ans = x[k - 1];
	}
	else if (x[n - 1] <= 0) {
		ans = x[n - k + 1];
	}
	else {
		ans = 9223372036854775807LL;
		for (int i = 0; i <= n - k; i++) {
			ll l = x[i];
			ll r = x[i + k - 1];
			ll tmp = min(abs(l) + abs(l - r), abs(l - r) + abs(r));
			ans = min(ans, tmp);
		}
	}
	cout << ans << endl;
	return 0;
}