#include <iostream>
using namespace std;

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