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

namespace yuki0045 {
    class Program {
        static internal List<int> V;
        static internal int FindMax(int k) {
            return V[ k - 1 ] + ( V.Count() - k <= 1 ? 0 : ( V.Count() - k == 2 ) ? V[ k + 1 ] : Math.Max( FindMax( k + 2 ), FindMax( k + 3 ) ) );
        }
        static internal int TakeMax(System.IO.TextReader reader) {
            V = reader.ReadLine().Split().ToList().ConvertAll( int.Parse );
            return V.Count == 1 ? V[ 0 ] : Math.Max( FindMax( 1 ), FindMax( 2 ) );
        }

        static void Main(string[] args) {
            Console.ReadLine();
            Console.WriteLine( TakeMax( Console.In ) );
        }
    }
}