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>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <math.h>
#include <limits.h>

int main(void){
    int n,k;
    scanf("%d%d",&n,&k);
    long long x[n];
    for (int i=0; i<n; i++){
        scanf("%lld",&x[i]);
    }
    
    long long tmp,ans=LLONG_MAX;
    for (int i=0; i+k-1<n; i++){
        
        if (x[i]*x[i+k-1]>=0){
            tmp=fmax(llabs(x[i]),llabs(x[i+k-1]));
            
            
            
            
        } else if (x[i]*x[i+k-1]<0){
            if ( x[i]*-2+ x[i+k-1] > x[i]*-1+ x[i+k-1]*2 ){
                tmp=x[i]*-1+ x[i+k-1]*2;
            } else {
                tmp=x[i]*-2+ x[i+k-1];
            }
        }
        
        
        
        
        
        if (ans>tmp){
            ans=tmp;
        }
    }
    printf("%lld\n",ans);
	return 0 ;
}