#include<iostream>

using namespace std;

int suma(int a[100], int s, int d)
{ if(s==d) return a[s];
  else return suma(a,s,(s+d)/2)+suma(a,(s+d)/2+1,d);
}

int main()
{
    int a[100],n,i;
    cin>>n;
    for(i=1;i<=n;i++) cin>>a[i];
    cout<<suma(a,1,n);
    system("pause");
    return 0;
}