MethodsDebugging&Troubleshootig Code - 06. Prime Checker

using System;
using System.Numerics;


namespace _04b_MethodsDebuggingTroubleshootingCode_Exercises
{
    class MethodsDebuggingTroubleshootingCode_Exercises
    {
      static void Main(string[] args)
        {
            long num = long.Parse(Console.ReadLine());
            Console.WriteLine(ReturnisPrime(num));
        }

        static bool ReturnisPrime(long num)
        {
            num = Math.Abs(num);
            if (num == 0) return false;
            if (num == 1) return false;
            if (num == 2) return true;

            for (long i = 2; i <= Math.Ceiling(Math.Sqrt(num)); ++i)
            {
                if (num % i == 0) return false;
            }
            return true;
        }
    }
}