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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;
#define all(a) (a).begin(),(a).end()
#define cinv(v,n) for(size_t i=0;i<(n);i++){cin>>(v)[i];}
#define nvec(type,v,n) vector<type> v(n);cinv(v,n)
#define npairs(type1,type2,v,n) vector<pair<type1,type2>> v(n);for(size_t i=0;i<(n);i++){cin>>v[i].first>>v[i].second;}
#define ntuples(type1,type2,type3,v,n) vector<tuple<type1,type2,type3>> v(n);for(size_t i=0;i<(n);i++){cin>>get<0>(v[i])>>get<1>(v[i])>>get<2>(v[i]);}

#define min_index(v) size_t(min_element(all(v))-(v).begin())
#define max_index(v) size_t(max_element(all(v))-(v).begin())
#define min_e(v) *min_element(all(v))
#define max_e(v) *max_element(all(v))

#define count_le(v,a) size_t(upper_bound(all(v),a)-(v).begin())
#define count_lt(v,a) size_t(lower_bound(all(v),a)-(v).begin())
#define count_ge(v,a) size_t((v).end()-lower_bound(all(v),a))
#define count_gt(v,a) size_t((v).end()-upper_bound(all(v),a))

#define order(neq_sl) [](const &auto s, const &auto l){return neq_sl;}
#define make_lr(v,type,l,r) vector<type> l(n+1),r(n+1);FOR(i,n){l[i+1]=l[i]+v[i];r[i+1]=r[i]+v[n-1-i];}

#define acm accumulate
#define SUM(v) acm(all(v),0l)

int main() {
  int n,k;
  cin>>n>>k;
  nvec(long, x, n);
  long x_=1000000000;
  for (size_t i = 0; i < n-(size_t)k+1; i++) {
    x_=min(x_,x[i+k-1]-x[i]+min(abs(x[i+k-1]),abs(x[i])));
  }
  cout<<x_;
}