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<bits/stdc++.h>
using namespace std;

int x[int(1e5)];

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N, K, x0 = -1;
    long cu_time, ans = long(1e9);
    cin >> N >> K;
    for(int n=0; n<N; n++){
        cin >> x[n];
        if(x[n] >= 0 && x0 == -1)x0 = n;
    }
    //cout << x0 << "\n";
    if(x0 > 0){
        if(K + x0 - 1 < N)ans = x[K+x0-1];
        for(int n=0; n<=x0-1; n++){
            if(2 * n >= K)cu_time = abs(x[n]);
            else {
                cu_time = 2 * abs(x[n]);
                cu_time += x[K+n-1];
            }
            //cout <<n << " " << cu_time << "\n";
            ans = min(ans, cu_time);
        }
    }
    else ans = abs(x[K-1]);
    cout << ans << "\n";
    return 0;
}