using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

class Magatro
{
    
    static void Main()
    {
        int N = int.Parse(Console.ReadLine());
        int[] V = Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();
        int[] counter = new int[N];
        counter[0] = V[0];
        if (N == 1)
        {
            Console.WriteLine(V[0]);
            return;
        }
        counter[1] = V[1];
        for(int i = 0; i < N; i++)
        {
            for(int j = i + 2; j < N; j++)
            {
                counter[j] = Math.Max(counter[j], counter[i] + V[j]);
            }
        }
        Console.WriteLine(counter.Max());
    }
}