#include <algorithm>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;

int main() {
  int n;
  cin >> n;
  cin.ignore();
  string line;
  getline(cin, line);
  istringstream iss(line);
  vector<int> value;
  string s;
  while (iss >> s) {
    value.push_back(stoi(s));
  }
  vector<int> dp(1001);
  dp[0] = 0;
  for (int i = 0; i < n; i++) {
    if (i <= 1)
      dp[i + 1] = max(dp[i], value[i]);
    else
      dp[i + 1] = max(dp[i - 1] + value[i], dp[i]);
  }

  cout << dp[n] << endl;

  return 0;
}