using System;
using System.Collections.Generic;
using System.Linq;

class P
{
    static int Search(int i)
    {
        int res = 0;
        if(i >= n)
        {
            res = 0;
        }
        else
        {
            res = Math.Max(Search(i + 2), Search(i + 3)) + V[i];
        }
        return res;
    }
    static int n;
    static int[] V = new int[1000];

    static void Main(string[]_)
    {
        n = int.Parse(Console.ReadLine());
        V = new int[n + 1];
        _=Console.ReadLine().Split(' ');
        for (int i = 0; i < n; i++)
        {
            V[i] = int.Parse(_[i]);
        }
        Console.WriteLine(Math.Max(Search(0),Search(1)));
    }
}