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

using namespace std;

int main() {
	int n;
	cin >> n;
	vector<int> v(n);
	for (int i = 0; i < n; ++i) {
		cin >> v[i];
	}
	vector<int> gain(n);
	gain[0] = v[0];
	if (n >= 2) {
		gain[1] = max(v[1], v[0]);
		for (int i = 2; i < n; ++i) {
			gain[i] = max(v[i] + gain[i - 2], gain[i - 1]);
		}
	}
	cout << gain[n - 1] << endl;
	return 0;
}