// Find the largest Prime factor of 600851475143
using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            // Declare Vars
            long primeFactorNumber = 600851475143;
            int finalNumber = 0;

            // Use variable i for calculations until reasonable estimated number, i should equal 2 to save cycles
            for (int i = 2; i < 100000; i++)
            {
                if (primeFactorNumber % i == 0)
                {
                    // Set instanced vars that I can work with
                    // numberToWorkWith should equal 2 to save cycles
                    int numberToWorkWith = 2;
                    bool notAPrime = false;

                    // As long as numberToWorkWith is less than 10k (reasonable limit for this exercise), and notAPrime isn't trigged
                    // Loop
                    while (numberToWorkWith < 10000 && !notAPrime)
                    {
                        // If i is divisble by the working number (numberToWorkWith), it's not a prime number---flag
                        if (i % numberToWorkWith == 0 && i != numberToWorkWith && i != 0)
                        {
                            notAPrime = true;
                        }

                        // Increment to further loop
                        numberToWorkWith++;
                    }

                    // If the conditions are met, then it's a prime number
                    if (!notAPrime)
                    {
                        finalNumber = i;
                    }
                }
            }
            Console.WriteLine("Finished.  Your final prime number is {0}", finalNumber);
            // Once finished, ensure program doesn't exit
            Console.ReadLine();
        }
    }
}