import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] calories = new int[n];
        for(int calories_i=0; calories_i < n; calories_i++){
            calories[calories_i] = in.nextInt();
        }
        // your code goes here
        int j =1;
        int sum =0;
        for(int calories_i=1; calories_i < n; calories_i++) {
            sum += calories[calories_i] * j;
            j = j << 1;
        }
      System.out.println(sum + (calories[0] *j));
        
    }
}