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 <math.h>
#define rep(i,l,r) for((i)=(l);(i)<(r);(i)++)
#define repm(i,l,r) for((i)=(l);(i)<(r);(i)--)
#define min(a,b) ((a)<(b)?(a):(b))
#define abs(a) ((a)>(0)?(a):-(a))
int main(){
    long long i,j,n,k,ans=10e9,buf=0,buf1,buf2,s;
    scanf("%lld%lld",&n,&k);
    long long x[n],sub[n];
    rep(i,0,n){
        scanf("%lld",&x[i]);
        if(k==1)ans=min(ans,abs(x[i]));
        if(i>0)sub[i-1]=abs(x[i]-x[i-1]);
    }
    if(k>1){
    rep(i,0,n-k+1){
        if(i==0)rep(j,0,k-1)buf+=sub[j];
        else buf=buf+sub[i+k-2]-sub[i-1];
        buf1=abs(x[i]);
        buf2=abs(x[i+k-1]);
        s=min(buf1,buf2);
        ans=min(buf+s,ans);
    }
    }
    printf("%lld",ans);
}