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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <stdlib.h>

int main()
{
	int i, N, K, x[100001];
	scanf("%d %d", &N, &K);
	for (i = 1; i <= N; i++) scanf("%d", &(x[i]));
	
	int ans = x[N] - x[1], b;
	if (x[1] >= 0) ans = x[K];
	else if (x[N] <= 0) ans = x[N-K+1];
	else {
		for (b = 1; x[b+1] < 0; b++);
		if (b >= K && -x[b-K+1] < ans) ans = -x[b-K+1];
		if (b + K <= N && x[b+K] < ans) ans = x[b+K]; 
		for (i = 1; i < K && i <= b && i >= b + K - N; i++) {
			if (x[b+K-i] - x[b-i+1] * 2 < ans) ans = x[b+K-i] - x[b-i+1] * 2;
			if (x[b+K-i] * 2 - x[b-i+1] < ans) ans = x[b+K-i] * 2 - x[b-i+1];
		}
	}
	
	printf("%d\n", ans);
	fflush(stdout);
	return 0;
}