using System;
using System.Linq;

namespace KaitenSushi
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            int[] P = Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();
            int R = MainProcess(N,P);
            Console.WriteLine(R);

        }

        private static int MainProcess(int N,int[] P)
        {
            int[] M = new int[N + 1];
            M[0] = 0;
            M[1] = P[0];
            for(int i = 2; i < N + 1; i++)
            {
                M[i] = Math.Max(M[i - 1], M[i - 2] + P[i - 1]);
            }
            return M[N];
        }
    }
}