#include <iostream>
#include <cstdint>
#include <vector>
#include <algorithm>

using namespace std;

int main() {

  ios::sync_with_stdio(false);
  cin.tie(0);

  int n;
  cin >> n;
  vector<int> v(n + 1, 0);
  for (int i = 1; i < n + 1; i++) {
    cin >> v.at(i);
  }
  for (int i = 2; i < n + 1; i++) {
    v.at(i) = max(v.at(i - 1), v.at(i) + v.at(i - 2));
  }

  cout << v.at(n) << endl;
  return 0;
}