#include <bits/stdc++.h>

using namespace std;

int n;
vector<int> v;
vector<int> sum;
int max_sum(int i) {
	if (sum[i] == -1) {
		int m = 0, m2 = 0;
		if (i + 2 < n)
			m = max_sum(i + 2);
		if (i + 3 < n)
			m2 = max_sum(i + 3);
		sum[i]=v[i] + max(m, m2);
	}
	return sum[i];
}

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

	return 0;
}