using System;

public class Program

{

    public static void Main()

    {

    long n;

            Console.WriteLine("Enter a positive integer:");

            n = int.Parse(Console.ReadLine());

            if (n < 2)

            { Console.WriteLine(n + "is not prime."); }

            else if (n < 4)

            { Console.WriteLine(n + "is prime."); }

            else if (n % 2 == 0)

            { Console.WriteLine(n + " = 2 *" + n / 2); }

            else

            {

                char prime = 'y'; 

                for (int d = 3; d <= n / 2; d += 2)

                {   

                    if (n % d == 0)

                    {

                        Console.WriteLine(n + " is divisible by " + d + " so it is not prime");

                        prime = 'n';

                        break;

                    }

​

                }

                if (prime == 'y') 

                Console.WriteLine(n + " is prime.");

            }

            Console.ReadLine();

​

}

}