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 <vector>
#include <algorithm>
#include <cstdlib>

using namespace std;

int main()
{
    int n, k; cin >> n >> k;
    vector<int> x(n);
    vector<int> ans(k * 2);

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

    int st = 0;
    while (x[st] < 0) ++st;
    int l = st - k;
    if (l < 0) l = 0;
    int r = st + k - 1;
    if (r > n-1) r = n-1;
    int idx = 0;
    for (int i = l; i < l + k; ++i) {
        ans[idx++] = abs(x[i]) + abs(x[i+k-1] - x[i]);
    }
    idx = k * 2 - 1;
    for (int i = r; i > r - k; --i) {
        ans[idx--] = abs(x[i]) + abs(x[i] - x[i-k+1]);
    }

    cout << *min_element(ans.begin(), ans.end()) << endl;

    return 0;
}