#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using ld = long double;

const ld pi = 3.14159265358979;
const int mod = 1000000007;

int main(){
	int n;
	cin >> n;
	vector<int> v(n + 100 , 0);
	for(int i = 0; i < n; i++){
		cin >> v[i];
	}
	vector<int> dp(1234 , 0);
	dp[0] = v[0];
	dp[1] = v[1];
	for(int i = 0; i < n; i++){
		for(int j = i + 2; j < n; j++){
			if(j >= n)continue;
			dp[j] = max(dp[j] , dp[i] + v[j]);
		}
	}
	cout << dp[n - 1] << endl;
 return 0;
}