using System;
using System.Linq;

namespace Program
{
    class Program
    {
        static void Main()
        {
            int count = int.Parse(Console.ReadLine());
            int[] aji = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            Dp m_dp = new Dp(aji, count);
            Console.WriteLine(m_dp.GetMax().ToString());
            Console.ReadLine();
        }

    }
    class Dp
    {
        private int[,] _dp = new int[1000, 2];
        private int[] _aji;
        private int _saraCount;

        public Dp(int[] aji, int saracount)
        {
            _saraCount = saracount;
            _aji = aji;
            _dp[0, 0] = 0;
            _dp[0, 1] = _aji[0];
        }

        public int GetMax()
        {
            if (_saraCount == 1)
            {
                return _aji[0];
            }
            _dp[1, 0] = _dp[0, 1];
            _dp[1, 1] = _aji[1] + _dp[0, 0];

            for (int count = 2; count < _saraCount; count++)
            {
                _dp[count, 0] = Math.Max(_dp[count - 1, 1], _dp[count - 2, 1]);
                _dp[count, 1] = _aji[count] + Math.Max(_dp[count - 1, 0], _dp[count - 2, 0]);
            }
            return Math.Max(_dp[_saraCount - 1, 0], _dp[_saraCount - 1, 1]);
        }
    }
}