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

class Program
{
    static string InputPattern = "Input5";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("4");
            WillReturn.Add("1 2 3 4");
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("4");
            WillReturn.Add("5 4 4 9");
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("7");
            WillReturn.Add("1 2 9 10 1 1 4");
        }
        else if (InputPattern == "Input4") {
            WillReturn.Add("1");
            WillReturn.Add("100");
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        int[] VArr = InputList[1].Split(' ').Select(X => int.Parse(X)).ToArray();
        int UB = VArr.GetUpperBound(0);

        //添字が皿の合計、値が美味しさ合計の最大値
        int[] SumVArr = new int[UB + 1];

        for (int I = 0; I <= UB; I++) {
            if (I == 0 || I == 1) {
                SumVArr[I] = VArr[I];
                continue;
            }

            //配列の添字の上限までの範囲での、最大値を返す
            Func<int, int> DeriveHaniMaxFunc = pJyougenInd =>
            {
                int WillReturn = SumVArr[0];
                for (int J = 0; J <= pJyougenInd; J++) {
                    if (WillReturn < SumVArr[J])
                        WillReturn = SumVArr[J];
                }
                return WillReturn;
            };

            //その皿を取るノードでの美味しさ合計の最大値
            int Node1SumV = DeriveHaniMaxFunc(I - 2) + VArr[I];
            //その皿を取らないノードでの美味しさ合計の最大値
            int Node2SumV = DeriveHaniMaxFunc(I - 1);

            SumVArr[I] = Math.Max(Node1SumV, Node2SumV);
        }
        Console.WriteLine(SumVArr.Max());
    }
}