#include <iostream>
using namespace std;

int *dp;
int *used;

int f(int i){
	if(i < 2) return 0;
	else{
		if(used[i] == 0){
			dp[i] = dp[i] + max(f(i-2), f(i-3));
			used[i] = 1;
		}
		return dp[i];
	}
}

int main() {
	int n, i;
	cin >> n;
	dp = new int [n+1];
	used = new int [n+1];
	for(i = 1; i<=n; ++i){
		cin >> dp[i];
		used[i] = 0;
	}
	f(n);
	cout << dp[n];
	return 0;
}