#include<iostream>
#include<algorithm>
using namespace std;

int n;
int v[1000];
int dp[1000];

int main() {
	cin >> n;
	for (int i = 0; i<n; i++) {
		cin >> v[i];
	}
	if (n == 1) {
		cout << v[0] << endl;
		return 0;
	}
	else if (n == 2) {
		cout << max(v[0], v[1]) << endl;
		return 0;
	}
	else if (n == 3) {
		cout << max(v[0] + v[2], v[1]) << endl;
		return 0;
	}
	else {
		dp[n - 3] = v[n - 3] + v[n - 1];
		dp[n - 2] = v[n - 2];
		dp[n - 1] = v[n - 1];
		for (int i = n - 4; i >= 0; i--) {
			dp[i] = max(dp[i + 2], dp[i + 3]) + v[i];
		}
		cout << max(dp[0], dp[1]) << endl;
		return 0;
	}
}