im a beginner. and learning c#. im trying to do my homework, but got stuck. my program will exit the loop even if i type wrong input : using System;
using static System.Console;


namespace GreenVille
{
    class Program
    {
        static void Main(string[] args)
        {
            int lastYear = 0, thisYear = 0, totalRev;

            while (lastYear >= 0 && lastYear <= 30)
            {
                WriteLine("Enter number contestants last year >> ");
                lastYear = int.Parse(ReadLine());
                lastYear++;
            }
            WriteLine("Number must be between 0 and 30");
            WriteLine("Enter number contestants last year >> ");

            while (thisYear >= 0 && thisYear <= 30)
            {
                WriteLine("Enter num contestants this year >> ");
                thisYear = int.Parse(ReadLine());
            }
            WriteLine("Number must be between 0 and 30");
            
            totalRev = thisYear * 25;
            
            WriteLine("last year's competition has {0} conts, and this year's has {1} conts " +
                "\nRevnue expected this year is {2} ", lastYear, thisYear, totalRev.ToString("c"));
            
            
            
            if (thisYear > lastYear && thisYear <= (lastYear * 2))
                WriteLine("The competition is bigger than ever!");
            else
                    if (thisYear < lastYear)
                WriteLine("A tighter race this year! Come out and cast our vote!!");
            else
                    if (thisYear > lastYear * 2)
                WriteLine("The competition is more than twice as big this year!");
        }
    }
}
