#include<iostream>
#include<algorithm>
using namespace std;
int main() {
	int n, v[1101], dp[1101] = {};
	cin >> n;
	for (int i = 1; i <= n; i++)cin >> v[i];
	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;
}