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: Accepted)

#include "iostream"
#include "algorithm"
#include "string"
#include "vector"
#include "cmath"
#include "bitset"
#include "queue"
#include "functional"
#include "map"
#include "unordered_map"
#include "set"
#include "stack"

#define lp(n) for (int i = 0; i < n; i++)
#define LP(n,i) for (int i = 0; i < n; i++)
#define mod 1000000007
#define sp ' '
#define intmax 2147483647
#define llmax 9223372036854775807
#define nya_n "(=^･ω･^=)"
typedef long long ll;
using namespace std;


/*
ll gcd(ll x, ll y) {
if (y == 0) return x;
return gcd(y, x%y);
}
/*
ll lcm(ll x, ll y) {
ll g = gcd(x, y);
return x / g * y;
}
ll pw(int x, int n) {
	ll y = 1;
	ll p = x;
	while (n != 0) {
		if (n % 2) {
			y = y*p%mod;
			n = n - 1;
		}
		else {
			p = p*p%mod;
			n = n / 2;
		}
	}
	return y;
}

ll modinv(ll x) {
	return pw(x, mod - 2);
}*/

ll n, x[100010], k, l, r, mn;
bool flag;

int main() {
	flag = false;
	l = r = llmax;
	cin >> n >> k;
	lp(n) {
		cin >> x[i];
		if (flag==false&&x[i] <= 0)l = i;
		if (flag == false && x[i] > 0) {
			r = i;
			flag = true;
		}
	}
	if (l == llmax) {
		cout << x[k - 1] << endl;
	}
	else if (r == llmax) {
		cout << -x[n - k] << endl;
	}
	else {
		mn = llmax;
		for (int i = r; i <= r + k - 1 &&i < n; i++) {
			if (i-k+1>=0)
				mn = min(mn, x[i]*2 - x[i - k + 1]);
		}
		for (int i = l; i >= l - k + 1 && i >= 0; i--) {
			if (i + k - 1 <= n - 1)
				mn = min(mn, -x[i] * 2 + x[i + k - 1]);
		}
		cout << mn << endl;
	}
	return 0;
}