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<math.h>
#define FOR(n) for(int i=0;i<n;i++)
#define FORJ(n) for(int j=0;j<n;j++)
#define PRN(n) printf("%d\n",n)
#define PRF(n) printf("%lf\n",n)
#define PRL(n) printf("%lld\n",n)
#define PRS(s) printf("%s\n",s)
#define PRC(c) printf("%c",c)
#define INF 1e10
#define mod 1000000007
typedef long long int ll;
ll z(ll a){
  if(a<0)a*=-1;
  return a;
}
int u(const void *a, const void *b){
    return *(ll*)a-*(ll*)b;
}
int d(const void *a, const void *b){
    return *(ll*)b-*(ll*)a;
}
int min(int a,int b){
  if(a>b)return b;
  return a;
}
int max(int a,int b){
  if(a>b)return a;
  return b;
}
ll gcd(ll a,ll b){
  if(!b)return a;
  return gcd(b,a%b);
}
int kt(ll a){
  int sum=0;
  while(a){
    a/=10;
    sum++;
  }
  return sum;
}
int ks(ll a){
  int sum=0;
  while(a){
    sum+=a%10;
    a/=10;
  }
  return sum;
}
int main(void){
  int n,k;
  scanf("%d %d",&n,&k);
  k--;
  ll a[n];
  FOR(n)scanf("%lld",&a[i]);
  qsort(a,n,sizeof(ll),u);
  ll ans=INF;
  FOR(n-k){
    ll x;
    if(a[i]*a[i+k]<0){
      x=2*min(-a[i],a[i+k])+max(-a[i],a[i+k]);
    }else{
      x=max(z(a[i]),z(a[i+k]));
    }
    ans=min(ans,x);
  }
  PRL(ans);
  return 0;
}