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 <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
int a[200005];
int main() {
    int n, k;
    scanf("%d%d", &n, &k);
    for (int i = 1; i <= n; ++i) cin >> a[i];
    int res = 0;
    for (int i = 1; i + k - 1 <= n; ++i) {
        int tmp = a[i + k - 1] - a[i];
        if (a[i + k - 1] >= 0 && a[i] <= 0) {
            tmp += min(-a[i], a[i + k - 1]);
        }
        if (a[i + k - 1] <= 0 && a[i] <= 0) {
            tmp = a[i];
        }
        if (a[i + k - 1] >= 0 && a[i] >= 0) tmp = a[i + k - 1];
        if (i == 1) res = tmp;
        else res = min(tmp, res);
    }
    cout << res;
    return 0;
}