C# prime numbers

using System;

namespace HelloWorld
{
public class Program
{
public static void Main(string[] args)
{
Console.WriteLine("Enter a number:");
long num = long.Parse(Console.ReadLine());

        bool isPrime = num > 1;
        long i = 2;

        while (i * i <= num && isPrime)
        {
            if (num % i == 0)
            {
                isPrime = false;
                Console.WriteLine(num + " is not a prime number because it is divisible by " + i);
            }
            else
            {
                Console.WriteLine(num + " is not divisible by " + i);
            }
            i++;
        }

        Console.WriteLine(num + (isPrime ? " is a prime number." : " is not a prime number."));
    }
}

}