using System;
using System.Collections.Generic;
using System.Text;
using sc = Scanner;
using System.Collections;


class Program
{
    static void Main(string[] args)
    {
        Solve();
#if DEBUG
        Console.WriteLine("終了するにはなにかキーを押して下さい...");
        Console.ReadKey();
#endif

    }

    static void Solve()
    {
        int n = sc.NextInt();
        int[] v = sc.NextIntArray();
        int[,] dp = new int[n+1, 2];

        for (int i = 1; i < n+1; i++)
        {
            dp[i,0] = dp[i-1,1];
            dp[i,1] = Math.Max(dp[i-1,0]+v[i-1],dp[i-1,1]);
        }
        Console.WriteLine(Math.Max(dp[n,0],dp[n,1]));
    }
 }



public static class Scanner
{
    public static string[] NextStrArray()
    {
        return Console.ReadLine().Split(' ');
    }

    public static long[] NextLongArray()
    {
        string[] s = NextStrArray();
        long[] a = new long[s.Length];
        for (int i = 0; i < a.Length; i++)
        {
            a[i] = long.Parse(s[i]);
        }
        return a;
    }
    public static int[] NextIntArray()
    {

        string[] s = NextStrArray();
        int[] a = new int[s.Length];
        for (int i = 0; i < a.Length; i++)
        {
            a[i] = int.Parse(s[i]);
        }
        return a;
    }
    public static int NextInt()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
            tmp += readData;
        }
        return int.Parse(tmp);
    }
    public static double NextDouble()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
            tmp += readData;
        }
        return double.Parse(tmp);
    }
    public static long NextLong()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
            tmp += readData;
        }
        return long.Parse(tmp);
    }
    public static double[] NextDoubleArray()
    {

        string[] s = NextStrArray();
        double[] a = new double[s.Length];
        for (int i = 0; i < a.Length; i++)
        {
            a[i] = double.Parse(s[i]);
        }
        return a;
    }
}