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>
#include <string.h>
#include <numeric>

using namespace std;

///////////////////////////////////////////
//const long long int INF = 1000000000000000000LL;
const long long int INF = 1000000;
using ll = long long int;
using vi = vector<int>;
using Vi = vector<long long int>;
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define rep(i,N) for(int i=0;i<N;i++)
auto max(auto x,auto y){if(x>y){return x;}else{return y;}}
auto min(auto x,auto y){if(x>y){return y;}else{return x;}}
template<class T>bool chmax(T &former, const T &b) { if (former<b) { former=b; return 1; } return 0; }
template<class T>bool chmin(T &former, const T &b) { if (b<former) { former=b; return 1; } return 0; }
template<class T>T sqar(T x){ return x*x; }
#define Sort(v) std::sort(v.begin(), v.end(), std::greater<decltype(    v[0])>()) //降順でVをソート
///////////////////////////////////////////

ll n,k;
ll box[100000001]={0};
int main(){
    cin>>n>>k;
    ll flag=0;//flag = 負の座標の個数
    rep(i,n){
        cin>>box[i];
        if(box[i]>=0 && flag!=0){
            flag= i;
        }
    }
    ll ans = INT64_MAX;
    for(int i=0;n-i>k-1;i++){
        ll mi,ma;
        mi = box[i]; ma = box[k+i-1];//k+i-1 < n
        if(mi<0){
            if(ma<0){
                ans = min(ans,-mi);
            }else{
                ans = min(ans,min(2*ma-mi,ma-2*mi));
            };
        }else{
            ans = min(ans,ma);
        }
    }
    cout<<ans<<endl;
    return 0;
}