using System;
using System.Linq;

class Program
{
    public static void Main(string[] args)
    {
        var n = int.Parse(Console.ReadLine());
        var vs = Console.ReadLine().Split(' ').Select(element => int.Parse(element)).ToArray();
        var dp = new int[n+1];
        dp[0] = 0;
        dp[1] = vs[0];
        for (int i = 2; i <= n; i++)
        {
            dp[i] = Math.Max(dp[i - 2] + vs[i - 1], dp[i - 1]);
        }
        Console.WriteLine(dp[n]);
    }
}