#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long n;
  cin >> n;
  long long a[n];
  for (int i = 0, ggdem = n; i < ggdem; ++i) cin >> a[i];
  long long yo = -1;
  for (int i = 0, ggdem = n; i < ggdem; ++i) {
    if (a[i] == -1) {
      yo = i;
    }
  }
  for (int i = 0, ggdem = yo + 1; i < ggdem; ++i) {
    a[i] = 0;
  }
  long long res = 0;
  for (long long i = 20; i >= 0; i--) {
    if ((1 << i) > n) continue;
    long long mini = 1e18, minid = -1;
    for (int j = (1 << i) - 1, ggdem = n; j < ggdem; ++j) {
      if (a[j] <= mini) {
        mini = a[j];
        minid = j;
      }
    }
    res += mini;
    a[minid] = 1e18;
  }
  cout << res;
  return 0;
}
