#include <iostream>
#include <fstream>

using namespace std;

int sum(int v[], int st, int dr)
{
    if(st == dr)
        return v[st];
    int mid, sSt, sDr;
    mid = (st + dr) / 2;
    // st, st+1, st+2, ..., mid
    // mid+1, mid+2, ..., dr
    sSt = sum(v, st, mid);
    sDr = sum(v, mid+1, dr);
    return sSt + sDr;
}

int main()
{
    int n, v[1001];
    cin >> n;
    for(int i = 1; i <= n; i++)
        cin >> v[i];
    cout << sum(v, 1, n);
    return 0;
}