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: Accepted)

#include<cstdio>
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cmath>
using namespace std;

#define rep(i,j) for(int i=0;i<(int)(j);++i)
typedef long long qword;
const int maxn = 1e5 + 10;
qword a[maxn];



inline void run(int N, int k) {
    rep(i,N) {
        cin >> a[i];
    }
    qword ans = 0x7fffffffff;
    for (int i = 0; i < N - k + 1; ++ i) {
        qword x = a[i], y = a[i + k - 1];
        if (1ll * x * y < 0) {
            ans = min(ans, 2 * abs(x) + abs(y));
            ans = min(ans, 2 * abs(y) + abs(x));
        } else {
            ans = min(ans, max(abs(x), abs(y)));
        }
    }
    cout << ans << endl;
}

int main() {
    int N, k;
    while (cin >> N >> k) {
        run(N, k);
      	return 0;
    }
}