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 <cstring>
#include <cmath>
#include <cctype>
#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <vector>
#include <string>
#include <stack>
#include <queue>
 
typedef long long LL;
using namespace std;
 
int n, k;
int a[100005];
 
int min(int x, int y){
	return x < y ? x : y;
}
 
int main()
{
	//freopen("in.txt", "r", stdin);
	//freopen("out.txt", "w", stdout);
 
	scanf("%d %d", &n, &k);
	for (int i = 1; i <= n; i++){
		scanf("%d", &a[i]);
		//if(a[i] < 0) a[i] = a[i] * 2;
	}
	int ans = 0x3f3f3f3f;
	for (int i = k; i <= n; i++){
		ans = min(ans, a[i] - a[i - k + 1] + min(abs(a[i]), abs(a[i - k + 1])));
	}
	printf("%d\n", ans);
 
	return 0;
}