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 Pascal (FPC 2.6.2) (judge verdict: Accepted)

var
  a,b:array[-100000..100000]of longint;
  i,n,k:longint;
  ans:qword;
Function min(x,y:longint):longint;
begin
  if x<y then exit(x) else exit(y);
end;
begin
  readln(n,k);
  for i:=1 to n do read(a[i]);
  ans:=maxlongint;
  for i:=1 to n-k+1 do
    begin
	  if a[i]<=0 then
	    begin
		  if a[i+k-1]<=0 then
		    ans:=min(ans,-a[i]) else
		  begin
		    ans:=min(ans,abs(a[i]-0)*2+abs(a[i+k-1]-0));
		    ans:=min(ans,abs(a[i]-0)+abs(a[i+k-1]-0)*2);
		  end;
		end else
		begin
		  ans:=min(ans,a[i+k-1]);
		end; 
	end;
  write(ans);
end.