using System;
using System.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Math;

class Program
{
    static void Main()
    {
        var n = int.Parse(ReadLine());
        var v = ReadLine().Split().Select(int.Parse).ToArray();
        var dp = new int[n, 2];
        dp[0, 0] = 0;
        dp[0, 1] = v[0];
        for (int i = 1; i < n; i++)
        {
            dp[i, 0] = Max(dp[i - 1, 0], dp[i - 1, 1]);
            dp[i, 1] = Max(dp[i - 1, 0] + v[i], dp[i - 1, 1]);
        }
        WriteLine(Max(dp[n - 1, 0], dp[n - 1, 1]));
    }
}