using System;

​

public class Euler3

{

    public static void Main()

    {

        const long numm = 600851475143;

        long largestFact = 0;

        long[] factors = new long[2];

        for (long i = 2; i * i < numm; i++)

        {

            if (numm % i == 0)

            { 

                factors[0] = i;

                factors[1] = numm / i;

                for (int k = 0; k < 2; k++)

                {

                    bool isPrime = true;

                    for (long j = 2; j * j < factors[k]; j++)

                    {

                        if (factors[k] % j == 0)

                        {

                            isPrime = false;

                            break;

                        }

                    }

​

                    if (isPrime && factors[k] > largestFact)

                    {

                        largestFact = factors[k];

                    }

                }

            }

        }

        Console.WriteLine("The largest factor is: " +largestFact);

    }

}