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 <iomanip>
#include <string>
#include <map>
#include <math.h>
#include <vector>
#include <algorithm>
#include <cstdio>
#include <set>
#include <queue>
#include <sstream>
#include <stack>
#include <deque>
#include <memory.h>
#include <cassert>
#include <ctime>
#include <climits>
#include <list>
#include <time.h>
#include <unordered_map>
#include <bitset>
#include <exception>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef unsigned long long ull;
#define pb push_back
#define mp make_pair
#define FILE "file"
#define lc v << 1
#define rc (v << 1) + 1
#define inf 1e+9
#define linf ll(1e+18)
#define dinf 1e+14

typedef long long ll;
#define pb push_back
#define mp make_pair

ll getAbs(ll x) {
    if (x >= 0) {
        return x;
    } else {
        return -x;
    }
}

void solve()
{
    int N, K;
    cin >> N >> K;
    
    vector<ll> ar(N);
    for (int i = 0 ; i < N ; i++) {
        cin >> ar[i];
    }
    
    ll ans = linf;
    for (int i = 0 ; i <= N-K ; i++) {
        ans = min(ans, (ar[i+K-1]-ar[i]) + min(getAbs(ar[i+K-1]), getAbs(ar[i])));
    }
    
    cout << ans;
}

int main()
{
    ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
  //  freopen("/Users/bekhzodsoliev/Desktop/C++/cp/cp/file.in", "r", stdin);freopen("/Users/bekhzodsoliev/Desktop/C++/cp/cp/file.out", "w", stdout);
    
    int t = 1;
    //cin >> t;
    
    while(t--)
    {
        solve();
    }
    
    return 0;
}