#include <bits/stdc++.h>

using namespace std;

int main()
{
  int num;
  cin >> num;

  vector<int> v(num + 3, 0);
  for (int i = 0; i < num; ++i)
  {
    int tmp;
    cin >> tmp;
    v[i] = tmp;
  }

  vector<int> vo;
  vector<int> vx;

  for (int i = 0; i < num; i += 3)
  {
    // oxo
    vo.push_back(v[i] + v[i + 2]);
    // xxo
    vo.push_back(v[i + 2]);
    // xox
    vx.push_back(v[i + 1]);
    // oxx
    vx.push_back(v[i]);
  }

  long long result_o = 0;
  long long result_x = 0;

  for (int i = 0; i < vo.size(); i += 2)
  {
    result_o += (vo[i] > vo[i+1]) ? vo[i] : vo[i+1];
    result_x += (vx[i] > vx[i+1]) ? vx[i] : vx[i+1];
  }

  cout << ((result_o > result_x) ? result_o : result_x) << endl;
}