#include <bits/stdc++.h>

using namespace std;

int n;
vector<int> v;
int max_sum(int i) {
	int m=0, m2=0;
	if(i+2<n)
		m = max_sum(i + 2);
	if(i+3<n)
		m2 = max_sum(i + 3);
	return v[i] + max(m,m2);
}

int main() {
	cin >> n;
	v.resize(n);
	for (int i = 0;i < n;i++) {
		cin >> v[i];
	}
	if (n > 1)
		cout << max(max_sum(0), max_sum(1)) << endl;
	else
		cout << max_sum(0) << endl;
	

	return 0;
}