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 <bits/stdc++.h>
using namespace std;

using i64=int64_t;

#define rep(i,x,y) for(i64 i=i64(x),i##_max_for_repmacro=i64(y); i<i##_max_for_repmacro; ++i)
#define debug(x) #x << "=" << (x)
 
#ifdef DEBUG
#define _GLIBCXX_DEBUG
#define print(x) std::cerr << debug(x) << " (L:" << __LINE__ << ")" << std::endl
#else
#define print(x)
#endif
 
const int inf=1.01e9;
const i64 inf64=4.01e18;
const double eps=1e-9;
 
template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec){
    os << "[";
    for (const auto &v : vec) {
        os << v << ",";
    }
    os << "]";
    return os;
}

void solve(){
    i64 N,K;
    cin >> N >> K;
    vector<i64> x(N);
    rep(i,0,N) cin >> x[i];

    i64 idx=N;
    rep(i,0,N){
        if(x[i]>=0){
            idx=i;
            break;
        }
    }

    i64 ans=inf64;
    if(idx>=K){
        ans=min(ans,x[idx-1]-x[idx-K]-x[idx-1]);
        print(ans);
    }
    if(N-idx>=K){
        ans=min(ans,x[K+idx-1]-x[idx]+x[idx]);
        print(ans);
    }
    for(int i=idx-1; i>=0; --i){
        if((idx-i)+N-idx<K) continue;
        i64 K_=K-(idx-i);
        ans=min(ans,(x[idx-1]-x[i]-x[idx-1])*2+(x[K_+idx-1]-x[idx]+x[idx]));
        print(i);
        print(ans);
    }
    rep(i,idx,N){
        if((i-idx+1)+idx<K) continue;
        i64 K_=K-(i-idx+1);
        ans=min(ans,(x[idx-1]-x[idx-K_]-x[idx-1])+(x[i]-x[idx]+x[idx])*2);
        print(i);
        print(ans);
    }

    cout << ans << endl;
}

int main(){
    std::cin.tie(0);
    std::ios::sync_with_stdio(false);
    cout.setf(ios::fixed);
    cout.precision(16);
    solve();
    return 0;
}