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>
#define ll long long
#define rep(i,a,b) for(long long i=a; i<b; i+=1)
#define repr(i,a,b) for(long long i=a; i<=b; i+=1)
#define vec vector<ll>
#define map map<string,int>
#define repa(p,A) for(auto p:A)
#define pb push_back
#define sort(a) sort(a.begin(),a.end())
#define reverse(a) reverse(a.begin(),a.end())
const double PI=acos(-1);
 
using namespace std;

int main( ) {
    ll N,K;
    cin>>N>>K;
    vec A(N);
    rep(i,0,N) {
        cin>>A[i];
    }
    ll a=100000000000000000;
    rep(i,0,N-K+1) {
        ll c=min(abs(A[i])+abs(A[i+K-1]-A[i]),abs(A[i+K-1])+abs(A[i+K-1]-A[i]));
        a=min(a,c);     
    }
    cout<<a<<endl;
    }