#include <bits/stdc++.h>
using namespace std;
const int M = 19, N = (1 << M);
int a[N];
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n;
  cin >> n;
  int id = -1;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] == -1) id = i;
  }
  int rem = n - id - 1;
  int t = 0;
  long long ans = 0;
  while (rem > 0) {
    int mn = n - 1;
    for (int i = n - 1; i >= n / (1 << t) - 1; i--)
      if (a[mn] > a[i]) mn = i;
    ans += a[mn];
    a[mn] = 1e9 + 10;
    rem -= n / (1 << (t + 1));
    t++;
    assert(t <= 20);
    cerr << t << " **** \n";
  }
  cout << ans << "\n";
}
