using static System.Math;
using System;

public class Hello
{
    public static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = Array.ConvertAll(line, int.Parse);
        if (n == 1) { Console.WriteLine(a[0]); goto end; }
        var dp = new int[n];
        dp[0] = a[0];
        dp[1] = Max(a[0], a[1]);
        for (int i = 2; i < n; i++)
            dp[i] = Max(dp[i - 1], dp[i - 2] + a[i]);
        Console.WriteLine(dp[n - 1]);
        end:;
    }
}