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

class Program
{
    static void Main()
    {
        int n = ri();
        var v = ria();

        var dp = new int[n];
        dp[0] = v[0];
        if (n > 1) dp[1] = Math.Max(v[0], v[1]);
        for (int i = 2; i < n; i++)
        {
            dp[i] = Math.Max(dp[i - 2] + v[i], dp[i - 1]);
        }

        Console.WriteLine(dp[n - 1]);
    }

    #region Scan
    static int ri() { return int.Parse(Console.ReadLine()); }
    static long rl() { return long.Parse(Console.ReadLine()); }
    static double rd() { return double.Parse(Console.ReadLine()); }
    static string rs() { return Console.ReadLine(); }
    static int[] ria() { return Console.ReadLine().Trim().Split().Select(int.Parse).ToArray(); }
    static long[] rla() { return Console.ReadLine().Trim().Split().Select(long.Parse).ToArray(); }
    static double[] rda() { return Console.ReadLine().Trim().Split().Select(double.Parse).ToArray(); }
    static string[] rsa() { return Console.ReadLine().Trim().Split(); }
    static void mul(out int a, out int b) { var arr = ria(); a = arr[0]; b = arr[1]; }
    static void mul(out int a, out int b, out int c) { var arr = ria(); a = arr[0]; b = arr[1]; c = arr[2]; }
    static void mul(out int a, out int b, out int c, out int d) { var arr = ria(); a = arr[0]; b = arr[1]; c = arr[2]; d = arr[3]; }
    static void mul(out long a, out long b) { var arr = rla(); a = arr[0]; b = arr[1]; }
    static void mul(out long a, out long b, out long c) { var arr = rla(); a = arr[0]; b = arr[1]; c = arr[2]; }
    static void mul(out long a, out long b, out long c, out long d) { var arr = rla(); a = arr[0]; b = arr[1]; c = arr[2]; d = arr[3]; }
    #endregion
    #region Math
    const int mod = 1000000007;
    static bool isprime(long n)
    {
        if (n < 2) return false;
        for (long i = 2; i * i <= n; i++)
            if (n % i == 0)
                return false;
        return true;
    }

    #endregion
}