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

namespace YukiCoder
{
    class Program
    {
        static int nMax;
        static int[] pvi;
        static int[] pvo;

        static int zzz(int ni)
        {
            if (ni >= nMax) return 0;
            int nn = pvo[ni];
            if (nn > 0) return nn;

            int na = zzz(ni + 1);
            int nb = zzz(ni + 2) + pvi[ni];

            return pvo[ni] = na > nb ? na : nb;
        }
        //--------------------------------------------------------------//
        static void Main(string[] args)
        {
            nMax = int.Parse(Console.ReadLine());
            pvi = Console.ReadLine().Split().Select(int.Parse).ToArray();
            pvo = new Int32[nMax + 1];

            int n = zzz(0);

            Console.WriteLine(n);
            Console.ReadLine();
        }
    }
}