Prime or Not

using System;
class IsPrimeNumber
{
    static void Main()
    {
        Console.Write("Enter positive integer number n<=100: ");
        int num = int.Parse(Console.ReadLine());
        int prime = 0;
        if ((num < 0) || (num > 100))
        {
            Console.WriteLine("You have entered invaled number.");
        }
        for (int check = 2; check < num; check++);
        {
            if (num % check == 0)
            {
                prime = prime + 1;
                Console.WriteLine("not prime");
            }

            else
            {
                Console.WriteLine("prime");
            }
        }
    }
}