#include <bits/stdc++.h>
using namespace std;

int main() {
  int N;
  cin >> N;
  vector<int> V(N);
  for (int i = 0; i < N; i++) cin >> V.at(i);
  vector<int> DP(N);
  DP.at(0) = V.at(0);
  if (N > 1) DP.at(1) = max(V.at(0), V.at(1));
  for (int i = 2; i < N; i++) DP.at(i) = max(DP.at(i - 1), DP.at(i - 2) + V.at(i));
  cout << DP.at(N - 1) << "\n";
}