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<math.h>

int getmin(int a,int b);

int main(){
    int n,k,r1,r2;
    scanf("%d %d",&n,&k);
    int x[n];
    int R[n];
    for(int i=0;i<n;i++){
        scanf("%d",&x[i]);
    }
    for(int j=0;j<n-k+1;j++){
        r1=abs(x[j])+abs(x[j]-x[k+j-1]);
        r2=abs(x[k+j-1])+abs(x[k+j-1]-x[j]);
        R[j]=getmin(r1,r2);
    }
    /*for(int i=0;i<n-k+1;i++){
        printf("R[%d]=%d ",i,R[i]);
    }
    printf("\n");*/
    for(int i=0;i<n-k+1;i++){
        for(int j=i+1;j<n-k+1;j++){
            if(R[i]>R[j]){
                int tmp=R[i];
                R[i]=R[j];
                R[j]=tmp;
            }
        }
    }
    /*for(int i=0;i<n-k+1;i++){
        printf("R[%d]=%d ",i,R[i]);
    }*/
    printf("%d",R[0]);
    return 0;
}

int getmin(int a,int b){
    int c;
    if(a>=b){
        c=b;
    }else{
        c=a;
    }
    return c;
}