c# not all code paths return a value

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


namespace PrimeFactorisation
{
    class Program
    {
        static int Main(string[] args)
        {
            Eratosthenes eratosthenes = new Eratosthenes();

            bool ok = true;

            while (ok)
            {

                if ((args == null) || (args.Length < 1))
                {
                    Console.WriteLine("Syntax: primes InputFile ");
                    Console.ReadKey();
                    return 1;
                }
                string InFile = args[0];              

                //
                Console.WriteLine("Reading from:{0}", InFile);
                  
              
                try
                {

                   string[] numbersList = File.ReadAllLines(InFile);

                    foreach (string number in numbersList)
                    {

                        int toFactorise;
                        ok = int.TryParse(number, out toFactorise);

                        if (ok && toFactorise >= 2)
                        {
                            StringBuilder factorList = new StringBuilder();

                            foreach (int factor in GetPrimeFactors(toFactorise, eratosthenes))
                            {
                                if (factorList.Length == 0)
                                    factorList.Append("Prime factor(s): ");
                                else
                                    factorList.Append(", ");
                                factorList.Append(factor);
                            }

                            Console.WriteLine(factorList);
                        }

                    }
                    
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                    Console.ReadKey();
                    return 2;
                }
                Console.WriteLine("Press Enter To Continue");
                Console.ReadKey();
                return 0;
            }
        }


        private static IEnumerable<int> GetPrimeFactors(int value, Eratosthenes eratosthenes)
        {
            List<int> factors = new List<int>();

            foreach (int prime in eratosthenes)
            {
                while (value % prime == 0)
                {
                    value /= prime;
                    factors.Add(prime);
                }

                if (value == 1)
                    break;
            }

            return factors;
        }
    }
}