#include <iostream>
#include <vector>
#include <algorithm>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using namespace std;

int main() {
	int n;
	cin >> n;
	vector<int> v(n);
	rep(i, n) cin >> v[i];

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

	cout << dp[n - 1] << "\n";

	return 0;
}