The Fair Nut lives in n story house. a_i people live on the i-th floor of the house. Every person uses elevator twice a day: to get from the floor where he/she lives to the ground (first) floor and to get from the first floor to the floor where he/she lives, when he/she comes back home in the evening. 

It was decided that elevator, when it is not used, will stay on the x-th floor, but x hasn't been chosen yet. When a person needs to get from floor a to floor b, elevator follows the simple algorithm: 

  * Moves from the x-th floor (initially it stays on the x-th floor) to the a-th and takes the passenger. 
  * Moves from the a-th floor to the b-th floor and lets out the passenger (if a equals b, elevator just opens and closes the doors, but still comes to the floor from the x-th floor). 
  * Moves from the b-th floor back to the x-th. 

The elevator never transposes more than one person and always goes back to the floor x before transposing a next passenger. The elevator spends one unit of electricity to move between neighboring floors. So moving from the a-th floor to the b-th floor requires |a - b| units of electricity.

Your task is to help Nut to find the minimum number of electricity units, that it would be enough for one day, by choosing an optimal the x-th floor. Don't forget than elevator initially stays on the x-th floor. 

Input

The first line contains one integer n (1 ≤ n ≤ 100) — the number of floors.

The second line contains n integers a_1, a_2, …, a_n (0 ≤ a_i ≤ 100) — the number of people on each floor.

Output

In a single line, print the answer to the problem — the minimum number of electricity units.

Examples

Input

3
0 2 1


Output

16

Input

2
1 1


Output

4

Note

In the first example, the answer can be achieved by choosing the second floor as the x-th floor. Each person from the second floor (there are two of them) would spend 4 units of electricity per day (2 to get down and 2 to get up), and one person from the third would spend 8 units of electricity per day (4 to get down and 4 to get up). 4 ⋅ 2 + 8 ⋅ 1 = 16.

In the second example, the answer can be achieved by choosing the first floor as the x-th floor.
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.*;
import java.io.*;
public class Contest1 {
	static Scanner sc=new Scanner(System.in);
static	PrintWriter out=new PrintWriter(System.out);

	public static void main(String[] args) throws IOException {
		int n=sc.nextInt();
		Integer a[]=new Integer[n];
		int sum=0;
		for (int i = 0; i < a.length; i++) {
			a[i]=sc.nextInt();
			sum+=a[i];
		}
		int sum2=0;
		int idx=0;
		for (int i = 0; i < a.length; i++) {
			sum2+=a[i];
			if(sum2>=sum/2) {
				idx=i;
				break;
			}
		}
		int sum1=0;
		for (int i = 0; i < a.length; i++) {
			if(a[i]==0) {
				continue;
			}
			if(idx==0&&i==0) {
				continue;
			}
			else if(idx==i) {
				sum1+=(i+1)*2*a[i];
				
				continue;
			}
			if(i==1) {
				int r1=(Math.abs(((idx-i))))*2;
				sum1+=(i)*2*a[i];
				sum1+=r1;
			continue;
			}
			int r1=(Math.abs(((idx-i))))*2;
			sum1+=(i+1)*2*a[i];
			sum1+=r1;
		}
		System.out.println(sum1);
		
	}
	

static TreeSet<Integer> set=new TreeSet<Integer>();
	   public static void primes(int n) {
	       boolean[] primes = new boolean[n + 1];
	       for (int i = 2; i < primes.length; i++) {
	           primes[i] = true;
	       }
	       int num = 2;
	       while (true) {
	           for (int i = 2;; i++) {
	               int multiple = num * i;
	               if (multiple > n) {
	                   break;
	               } else {
	                   primes[multiple] = false;
	               }
	           }
	           boolean nextNumFound = false;
	           for (int i = num + 1; i < n + 1; i++) {
	               if (primes[i]) {
	                   num = i;
	                   nextNumFound = true;
	                   break;
	               }
	           }
	           if (!nextNumFound) {
	               break;
	           }
	       }
	       for (int i = 0; i < primes.length; i++) {
	           if (primes[i]) {
	           set.add(i);
	           }
	       }
	   }
 }
 class Scanner{
    StringTokenizer st;
    BufferedReader br;
    public Scanner(InputStream system){
        br=new BufferedReader(new InputStreamReader(system));
    }
    public Scanner (String file) throws IOException{
        br=new BufferedReader(new FileReader(file));
    }
    public String next() throws IOException{
        while (st==null || !st.hasMoreTokens())
            st=new StringTokenizer(br.readLine());
        return st.nextToken();
    }
    public  String nextLine() throws IOException{
        return br.readLine();

    }
    public int nextInt() throws IOException{
        return Integer.parseInt(next());

    }
    public long nextLong() throws IOException{
        return Long.parseLong(next());

    }
    public Double nextDouble() throws IOException{
        return Double.parseDouble(next());
        

    }
 }
