PrimeNumberCheck

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace PrimeNumbers
{
    class PrimeNumbers
    {
        static void Main()
        {
            int num;

            Console.WriteLine("Enter number: ");
            num = int.Parse(Console.ReadLine());
            if (num == 0 || num == 1)
            {
                Console.WriteLine(num + " is not a prime number");
                Console.ReadLine();
            }
            else
            {
                for (int a = 2; a <= Math.Sqrt(num); a++)
                {
                    if (num % a == 0)
                    {
                        Console.WriteLine(num + " is not a prime number");
                        return;
                    }

                }
                Console.WriteLine(num + " is a prime number");
            }
        }
    }
}