using System; using System.Collections; using System.Collections.Generic; using System.IO; using System.Linq; using System.Numerics; using System.Text; using static System.Console; using static System.Convert; using static System.Math; using static Extentions; class IO { int idx; string[] input; public IO(TextReader reader) { input = reader.ReadToEnd().Split(new[] { " ", "\n", "\r" }, StringSplitOptions.RemoveEmptyEntries); } T Get(Func parser) => parser(input[idx++]); public string S => Get(s => s); public char C => Get(char.Parse); public int I => Get(int.Parse); public long L => Get(long.Parse); public double F => Get(double.Parse); public decimal D => Get(decimal.Parse); public BigInteger B => Get(BigInteger.Parse); T[] Gets(int n, Func parser) => input.Skip((idx += n) - n).Take(n).Select(parser).ToArray(); public string[] Ss(int n) => Gets(n, s => s); public char[] Cs(int n) => Gets(n, char.Parse); public int[] Is(int n) => Gets(n, int.Parse); public long[] Ls(int n) => Gets(n, long.Parse); public double[] Fs(int n) => Gets(n, double.Parse); public decimal[] Ds(int n) => Gets(n, decimal.Parse); public BigInteger[] Bs(int n) => Gets(n, BigInteger.Parse); public void Write(params T[] xs) => WriteLine(string.Join(" ", xs)); public void Write(params object[] xs) => WriteLine(string.Join(" ", xs)); } static class Extentions { } static class Program { public static void Main() { var sw = new StreamWriter(OpenStandardOutput()) { NewLine = "\n" }; #if DEBUG sw.AutoFlush = true; #else sw.AutoFlush = false; #endif SetOut(sw); Solve(new IO(In)); Out.Flush(); } static void Solve(IO io) { var n = io.I; var v = io.Is(n); var dp0 = 0; var dp1 = v[0]; for (var i = 1; i < n; i++) { var dp2 = Max(dp1, dp0 + v[i]); dp0 = dp1; dp1 = dp2; } io.Write(dp1); } }