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: Wrong Answer)

#include<cstdio>

template<class _Tp>
	inline _Tp Abs(const _Tp&v)
		{return v<0?-v:v;}

template<class _Tp>
	inline _Tp Min(const _Tp&x,const _Tp&y)
		{return x<y?x:y;}
template<class _Tp>
	inline void chkMin(_Tp&x,const _Tp&y)
		{if(x>y)x=y;}

namespace IOManager{
	constexpr int FILESZ(131072);
	unsigned char buf[FILESZ];
	const unsigned char*ibuf=buf,*tbuf=buf;

	struct IOManager{

		IOManager(){}
		~IOManager(){}

		inline unsigned char gc()
			{return(ibuf==tbuf)&&(tbuf=(ibuf=buf)+fread(buf,1,FILESZ,stdin),ibuf==tbuf)?EOF:*ibuf++;}

		template<class _Tp>
			inline operator _Tp(){
				_Tp s=0u;unsigned char c=gc(),w=0;
				for(;c<48;c=gc())
					(c==45)&&(w=1);
				for(;c>47;c=gc())
					s=(_Tp)(s*10u+c-48u);
				return w?-s:s;
			}
	};
}IOManager::IOManager io;

int x[100001];

inline int calc(const int&l,const int&r)
	{return(r<=0)?-l:(0<=l?r:((r-l)+Min(Abs(l),Abs(r))));}

int main(){
	const int n=io,k=io;
	for(int i=1;i<=n;++i)
		x[i]=io;

	int Ans=x[n]-x[1];
	for(int i=1;i+k<=n+1;++i)
		chkMin(Ans,calc(x[i],x[i+k-1]));
	printf("%d",Ans);
}