#include <bits/stdc++.h>

using namespace std;

int main() {
	int n;
	cin >> n;
	vector<int> v(n+3), dp(n+3);
	for (int i = 0;i < n;i++) {
		cin >> v[i];
	}
	for (int i = 0;i < 3;i++) {
		v[n + i] = 0;
		dp[i] = v[i];
	}
	for (int i = 0;i < n-3;i++) {
		dp[i + 3] = max({dp[i+2], dp[i + 1]+v[i+3], dp[i] + v[i + 3] });
	}
	cout << dp[n - 1] << endl;

	return 0;
}