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 <bits/stdc++.h>
#define ll long long
using namespace std;
ll a[100005];
int main(){
	int n,k;
	scanf("%d%d",&n,&k);
	for (int i=1;i<=n;i++) scanf("%lld",&a[i]);
	int cc=0;
	for (int i=1;i<=n;i++)
		if (a[i]>0){
			cc=i;
			break;
		}
	if (cc==1){
		printf("%lld\n",a[k]);
		return 0;
	}
	ll ans=200000000000000;
	int t=1,w=k;
	while (w<=n){
		ll sum=0;
		if (a[t]<0) sum-=2*a[t];
		if (a[w]<0) sum-=a[w]; else sum+=a[w];
		ans=min(ans,sum);
		t++;w++;
		if (a[t]>=0) break;
	}
	printf("%lld",ans);
}