#pragma warning disable IDE1006
#pragma warning disable IDE0011
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Numerics;
using System.Text;
using static System.Convert;
using static System.Math;
using static Extentions;

class IO
{
    int idx;
    string[] line;

    public void R(params char[] sep) { line = Console.ReadLine().Split(sep); idx = 0; }
    public string S => line[idx++];
    public string[] Ss => line.Skip(idx++).ToArray();
    public char C => char.Parse(line[idx++]);
    public char[] Cs => line.Skip(idx++).Select(char.Parse).ToArray();
    public int I => int.Parse(line[idx++]);
    public int[] Is => line.Skip(idx++).Select(int.Parse).ToArray();
    public long L => long.Parse(line[idx++]);
    public long[] Ls => line.Skip(idx++).Select(long.Parse).ToArray();
    public double F => double.Parse(line[idx++]);
    public double[] Fs => line.Skip(idx++).Select(double.Parse).ToArray();
    public decimal D => decimal.Parse(line[idx++]);
    public decimal[] Ds => line.Skip(idx++).Select(decimal.Parse).ToArray();
    public BigInteger B => BigInteger.Parse(line[idx++]);
    public BigInteger[] Bs => line.Skip(idx++).Select(BigInteger.Parse).ToArray();

    public void Write<T>(params T[] xs)
    {
        Console.Write(xs.First());
        foreach (var x in xs.Skip(1)) Console.Write(" " + x);
        Console.WriteLine();
    }
    public void Write(params object[] xs)
    {
        Console.Write(xs.First());
        foreach (var x in xs.Skip(1)) Console.Write(" " + x);
        Console.WriteLine();
    }
}

static class Extentions
{
}

static class Program
{
    public static void Main()
    {
#if !DEBUG
        Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
#endif
        Solve(new IO());
        Console.Out.Flush();
    }

    public static void Solve(IO io)
    {
        io.R();
        var n = io.I;
        io.R();
        var v = io.Is;

        var dp = new int[n, 2];

        dp[0, 0] = 0;
        dp[0, 1] = v[0];

        for (var i = 1; i < n; i++)
        {
            dp[i, 0] = dp[i - 1, 1];
            dp[i, 1] = Max(dp[i - 1, 1], dp[i - 1, 0] + v[i]);
        }

        io.Write(Max(dp[n - 1, 0], dp[n - 1, 1]));
    }
}