#include <bits/stdc++.h>
using namespace std;
const long long INF = (long long)1e15 + 696969;
long long n, k;
long long a[1LL << 20], b[1LL << 20];
long long opt[20][1LL << 20];
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  memset(opt, -1, sizeof opt);
  cin >> n;
  for (long long i = 1; i < n; i <<= 1) k++;
  long long ok = false;
  for (long long i = 0; i < n; i++) {
    long long x;
    cin >> x;
    if (x == -1)
      ok = true;
    else if (!ok)
      a[i] = 0;
    else
      a[i - 1] = x;
  }
  n--;
  reverse(a, a + n);
  for (long long i = k - 1, j = 0; i > 0; i--) {
    j += 1 << i;
    b[i] = j;
  }
  for (long long i = 0; i < n; i++) {
    opt[0][i] = a[i];
  }
  for (long long i = 1; i < k; i++) {
    long long mn = INF;
    for (long long j = n - 1; j >= 0; j--) {
      if (j > b[i])
        opt[i][j] = INF;
      else {
        opt[i][j] = mn + a[j];
        mn = min(mn, opt[i - 1][j]);
      }
    }
  }
  cout << opt[k - 1][0] << endl;
  return 0;
}
