using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;

partial class Solver
{

    public void Run()
    {
        var N = ni();
        var s = ni(N);

        long ans = 0;
        var visited = new BooleanArray(N);

        for (int d = 1; d <= N - 1; d++)
        {
            visited.Clear();

            var begin1 = 0;
            var begin2 = (N - 1);

            long sub = 0;
            while (d <= begin2 && begin1 < N - d)
            {
                if (begin1 == begin2) break;
                if (visited[begin1]) break;
                visited[begin1] = true;
                if (visited[begin2]) break;
                visited[begin2] = true;
                sub += s[begin1];
                sub += s[begin2];
                ans = Math.Max(ans, sub);
                begin1 += d;
                begin2 -= d;
            }
        }

        cout.WriteLine(ans);
    }
}

public class BooleanArray
{
    private int[] array;
    private int trueValue = 1;

    public BooleanArray(int size)
    {
        array = new int[size];
    }

    public void Clear()
    {
        trueValue++;
    }

    public bool this[int index]
    {
        get
        {
            return array[index] == trueValue;
        }
        set
        {
            array[index] = value ? trueValue : trueValue - 1;
        }
    }

    public int Length
    {
        get
        {
            return array.Length;
        }
    }
}


// PREWRITEN CODE BEGINS FROM HERE
partial class Solver : Scanner
{
    public static void Main(string[] args)
    {
        new Solver(Console.In, Console.Out).Run();
    }

    TextReader cin;
    TextWriter cout;

    public Solver(TextReader reader, TextWriter writer)
        : base(reader)
    {
        this.cin = reader;
        this.cout = writer;
    }
    public Solver(string input, TextWriter writer)
        : this(new StringReader(input), writer)
    {
    }

    public int ni() { return NextInt(); }
    public int[] ni(int n) { return NextIntArray(n); }
    public long nl() { return NextLong(); }
    public long[] nl(int n) { return NextLongArray(n); }
    public double nd() { return NextDouble(); }
    public string ns() { return Next(); }
}

public class Scanner
{
    private TextReader Reader;
    private Queue<String> TokenQueue = new Queue<string>();
    private readonly CultureInfo ci = CultureInfo.InvariantCulture;

    public Scanner()
        : this(Console.In)
    {
    }

    public Scanner(TextReader reader)
    {
        this.Reader = reader;
    }

    public int NextInt() { return Int32.Parse(Next(), ci); }
    public long NextLong() { return Int64.Parse(Next(), ci); }
    public double NextDouble() { return double.Parse(Next(), ci); }
    public string[] NextArray(int size)
    {
        var array = new string[size];
        for (int i = 0; i < size; i++) array[i] = Next();
        return array;
    }
    public int[] NextIntArray(int size)
    {
        var array = new int[size];
        for (int i = 0; i < size; i++) array[i] = NextInt();
        return array;
    }

    public long[] NextLongArray(int size)
    {
        var array = new long[size];
        for (int i = 0; i < size; i++) array[i] = NextLong();
        return array;
    }

    public String Next()
    {
        if (TokenQueue.Count == 0)
        {
            if (!StockTokens()) throw new InvalidOperationException();
        }
        return TokenQueue.Dequeue();
    }

    public bool HasNext()
    {
        if (TokenQueue.Count > 0)
            return true;
        return StockTokens();
    }

    private bool StockTokens()
    {
        while (true)
        {
            var line = Reader.ReadLine();
            if (line == null) return false;
            var tokens = line.Trim().Split(" ".ToCharArray(), StringSplitOptions.RemoveEmptyEntries);
            if (tokens.Length == 0) continue;
            foreach (var token in tokens)
                TokenQueue.Enqueue(token);
            return true;
        }
    }
}


Measured memory_bytes: 31212