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 (Clang 3.8.0) (judge verdict: Wrong Answer)

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h>
#include <ctype.h>
#include <stdint.h>
#include <string.h>
#include <wchar.h>
#include <math.h>

#define MIN(a, b) ((a) < (b) ? (a) : (b))
#define MAX(a, b) ((a) > (b) ? (a) : (b))
#define ABS(a) ((a) >= 0 ? (a) : (-(a)))
#define ABSS(a, b) ((a) > (b) ? (a) - (b) : (b) - (a))

int compare_f(const void *a, const void *b) {
	return *((size_t *)a) > *((size_t *)b) ? -1 : 1;
}

static size_t comb(const size_t n, const size_t r) {
	size_t result = 1;

	for (size_t i = 0; i < r; i++) {
		result *= n - i;
		result /= i + 1;
	}

	return result;
}

static size_t countDivisors(const size_t n)
{
	size_t count = 1;

	for (size_t i = 2; i <= n; i++) {
		if (n%i == 0) {
			count++;
		}
	}

	return count;
}

static int32_t x[100000];

int main(void) {
	size_t N, K;

	scanf("%zu %zu\n", &N, &K);
	for (size_t idx = 0; idx < N; idx++) {
		scanf("%"PRId32, &x[idx]);
		if (idx < N - 1) {
			scanf(" ");
		}
	}

	size_t minTime = (size_t)UINT32_MAX;

	for (size_t beginIdx = 0; beginIdx <= N - K; beginIdx++) {
		const size_t endIdx = beginIdx + K - 1;
		if (x[beginIdx] * x[endIdx] < 0) {
			{
				const size_t timeCost = 2 * (size_t)ABS(x[beginIdx]) + (size_t)ABS(x[endIdx]);
				if (timeCost < minTime) {
					minTime = timeCost;
				}
			}
			{
				const size_t timeCost = (size_t)ABS(x[beginIdx]) + 2 * (size_t)ABS(x[endIdx]);
				if (timeCost < minTime) {
					minTime = timeCost;
				}
			}
		}
		else if (beginIdx == 0 && 0 <= x[beginIdx]) {
			const size_t timeCost = (size_t)ABS(x[endIdx]);
			if (timeCost < minTime) {
				minTime = timeCost;
			}
		}
		else if (endIdx == N - 1 && x[endIdx] <= 0) {
			const size_t timeCost = (size_t)ABS(x[beginIdx]);
			if (timeCost < minTime) {
				minTime = timeCost;
			}
		}
	}

	printf("%zu\n", minTime);

	return 0;
}