#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>

using namespace std;

int main() {
	int n;

	cin >> n;
	vector<int> v(n + 1, 0), dp(n + 1, 0);
	for (int i = 1; i <= n; i++) {
		cin >> v[i];
	}

	dp[0] = 0;
	dp[1] = v[1];
	for (int i = 2; i <= n; i++) {
		dp[i] = max(dp[i - 1], dp[i - 2] + v[i]);
	}

	cout << dp[n] << endl;
	return 0;
}