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 JavaScript (node.js v5.12) (judge verdict: Wrong Answer)

function main(input) {
  var N = input[0].split(" ")[0]-0;
  var K = input[0].split(" ")[1]-0;
  var list = input[1].split(" ").map(v=>v-0);
  var left = [];
  var right = [0];
  for(var i=0;i<N;i++){
    var v = list[i];
    if(v<0){
      left.push(v);
    }else if(v>0){
      right.push(v);
    }else{
      K--;
    }
  }
  left.push(0);
  left.reverse();
  var ans = null;
  for(var i=0;i<=K;i++){
    if(left[i] && right[K-i]){
      var a = 0;
      a+= Math.abs(left[i]*2) + Math.abs(right[K-i]);
      if(ans===null) ans = a;
      else ans = Math.min(a, ans);
    }
    if(left[K-i] && right[i]){
      var a = 0;
      a+= Math.abs(right[i]*2) + Math.abs(left[K-i]);
      if(ans===null) ans = a;
      else ans = Math.min(a, ans);
    }
  }

  if(K==0) console.log(0);
  else console.log(ans);
}
main(require('fs').readFileSync('/dev/stdin', 'utf8').trim().split("\n"))