#include<iostream>
#include<algorithm>
using namespace std;

int n;
int v[1000];
int memo[1000] = { 0 };

int dfs(int i) {
	if (i > n) return 0;
	if (memo[i] != 0) return memo[i];
	else {
		memo[i] = max(dfs(i + 2) + v[i], dfs(i + 3) + v[i]);
		return max(dfs(i + 2) + v[i], dfs(i + 3) + v[i]);
	}
}

int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> v[i];
	}
	cout << max(dfs(0), dfs(1)) << endl;
}