#include <fstream>
#define N 1001
using namespace std;

ifstream fin("ssm.in");
ofstream fout("ssm.out");

int main(){
    int v[N];
    int n, g, k = 2, max = -100, s = 0, j;
    fin>>n;
    for(int i = 1; i <= n; ++i)
        fin>>v[i];
    for(int i = 1; i <= n-1; ++i){
            g = 0;
        j = 1;
        while(g < n - i){
                while(j <= k){
                        s += v[j];
                        ++j;
                }
                if(s > max)
                    max = s;
                j=1;
                j += k;
                k += k;
                ++g;
        }
        ++k;
    }
    fout<<s;
}