zeroOne.cs

using System;
using System.Globalization;
using System.Linq;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var input = Console.ReadLine();
            
            try
            {
                if (IsValid(input))
                {
                    var result = GetLowestMultipleThatIsZeroOne(input);
                    Console.WriteLine(result);
                }
                else
                {
                    Console.WriteLine("Invalid input: Enter a number between 0 and 100000 exclusive.");
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

            // Keep the console open in debug mode.
            Console.WriteLine("Press any key to exit.");
            Console.ReadKey();   
        }

        /// <summary>
        /// Returns the lowest multiple of a number that is only zero's or one's
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        private static object GetLowestMultipleThatIsZeroOne(string input)
        {
            var n = Convert.ToInt32(input);
            var zeroOne = n;

            while (!zeroOne.ToString(CultureInfo.InvariantCulture).All(c => c == '0' || c == '1'))
            {
                zeroOne += n;
            }
            return zeroOne;
        }

        private static bool IsValid(string input)
        {
            var n = Convert.ToInt32(input);
            return 0 < n && n < 100000;
        }
    }
}