using System;

​

public class Program

{

    public static void Main()

    {

        Console.Write("X= ");

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

        bool isPrime = true;

​

        // Handle special case for x = 2

        if (x == 2)

        {

            Console.WriteLine("2 is a prime number");

            return;

        }

​

        if (x < 2 || x % 2 == 0)

        {

            isPrime = false;

        }

        else

        {

            for (int i = 3; i <= Math.Sqrt(x); i += 2)

            {

                if (x % i == 0)

                {

                    isPrime = false;

                    break;

                }

            }

        }

​

        if (isPrime)

            Console.WriteLine("{0} is a prime number",x);

        else

            Console.WriteLine("{0} is not a prime number",x);

    }

}

​