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: Accepted)

#include<stdio.h>
#define min(rhs,lhs) ((rhs)<(lhs)?(rhs):(lhs))
#define iabs(num) ((num) < 0 ? (-(num)):(num))
#include<limits.h>

int main(void){
    register int i;
    int n,k;
    scanf("%d %d",&n,&k);
    long x[n];
    for(i = 0;i < n;i++)scanf("%ld",&x[i]);
    long dist[n-k+1];
    for(i = 0;i < n-k+1;i++)dist[i] = iabs(x[i+k-1] - x[i]) + min(iabs(x[i+k-1]),iabs(x[i]));
    long ans = LONG_MAX;
    for(i = 0;i < n-k+1;i++)ans = min(ans,dist[i]);
    printf("%ld",ans);
}