#include <iostream>
#include <unordered_map>
using namespace std;
int n;
int v[1000];
unordered_map<int, int> memo[1000];
int solve(int i, int sum)
{
    if(i >= n)
        return sum;
    if(memo[i].count(sum) > 0)
        return memo[i][sum];
    return memo[i][sum] = max(solve(i + 2, sum + v[i]), solve(i + 3, sum + v[i]));
}
int main(void)
{
    cin >> n;
    for(int i = 0; i < n; i++)
        cin >> v[i];
    cout << max(solve(2, 0), max(solve(0, 0), solve(1, 0))) << endl;
    return 0;
}