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.*;
import java.math.*;
import java.security.*;
import java.text.*;
import java.util.*;
import java.util.concurrent.*;
import java.util.regex.*;

public class Main {

  static long MOD = 998244353;

  public static void main(String[] args) throws IOException {
    StringBuilder sb = new StringBuilder();
    FastInput fi = new FastInput(System.in);

    int n = fi.nextInt();
    long[] arr = new long[n + 1];

    for(int i = 1; i<=n; i++) {
      arr[i] = fi.nextInt();
    }

    long min = (long)1e18;

    for(int x= 1; x<=n; x++) {
      long temp = 0;
      for(int i = 1; i<=n; i++) {
        int diff = Math.abs(x-i);
        temp  += (diff + (i - 1) + (x-1) ) * arr[i];
      }
      min = Math.min(min, temp*2);
    }

    System.out.println(min);

  }
  private static class FastInput {

    BufferedReader  reader;
    StringTokenizer st;

    public FastInput(InputStream inputStream) {
      reader = new BufferedReader(new InputStreamReader(inputStream), 32768);
    }

    String nextString() {
      while(st == null || !st.hasMoreTokens()) {
        try {
          st = new StringTokenizer(reader.readLine());
        } catch (IOException e) {
          throw new RuntimeException(e);
        }
      }
      return st.nextToken();
    }

    int nextInt() {
      return Integer.parseInt(nextString());
    }

    long nextLong() {
      return Long.parseLong(nextString());
    }
  }
}
