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: Accepted)

function Main(input) {
    input = input.split("\n");
    var nk = input[0].split(" ");
    var n = parseInt(nk[0], 10);
    var k = parseInt(nk[1], 10);
    var X = input[1].split(" ").map(x => parseInt(x, 10));
    var zeroInd = -1;
    for (var i = 0; i < n; i++) {
        if (X[i] >= 0) {
            zeroInd = i;
            break;
        }
    }
    if (X[n-1] < 0) {
        zeroInd = n;
    }
    var left = Math.max(zeroInd - k, 0);
    var right = Math.min(zeroInd + k, n);
    var sofar = 1000000001;
    for (var i = left; i < right-k+1; i++) {
        var leftHalf = 0;
        var rightHalf = 0;
        if (i < zeroInd) {
            leftHalf = Math.abs(X[i]);
            rightHalf = Math.max(X[i+k-1], 0);
        } else if (i >= zeroInd) {
            leftHalf = 0;
            rightHalf = X[i+k-1];
        }
        var candid = Math.min(leftHalf*2+rightHalf, leftHalf+rightHalf*2)
        sofar = Math.min(sofar, candid);
    }
    console.log(sofar);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));