0-100

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

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
            int num = int.Parse(Console.ReadLine());
            int firstNum = num / 10;
            int secNum = num % 10;
            int bothNum = num;

            string firstWord = "";
            string secWord = "";
            string bothWord = "";

            switch (secNum)
            {

                case 1:
                    secWord = "one";
                    break;
                case 2:
                    secWord = "two";
                    break;
                case 3:
                    secWord = "three";
                    break;
                case 4:
                    secWord = "four";
                    break;
                case 5:
                    secWord = "five";
                    break;
                case 6:
                    secWord = "six";
                    break;
                case 7:
                    secWord = "seven";
                    break;
                case 8:
                    secWord = "eight";
                    break;
                case 9:
                    secWord = "nine";
                    break;
                default:
                    break;
            }
            switch (firstNum)
            {
                case 2:
                    firstWord = "twenty";
                    break;
                case 3:
                    firstWord = "thirty";
                    break;
                case 4:
                    firstWord = "fourty";
                    break;
                case 5:
                    firstWord = "fifty";
                    break;
                case 6:
                    firstWord = "sixty";
                    break;
                case 7:
                    firstWord = "seventy";
                    break;
                case 8:
                    firstWord = "eighty";
                    break;
                case 9:
                    firstWord = "ninety";
                    break;
                default:
                    break;
            }
                switch(bothNum)
            {
                case 10:
                    bothWord = "ten";
                    break;
                case 11:
                    bothWord = "eleven";
                    break;
                case 12:
                    bothWord = "twelve";
                    break;
                case 13:
                    bothWord = "thirteen";
                    break;
                case 14:
                    bothWord = "fourteen";
                    break;
                case 15:
                    bothWord = "fifteen";
                    break;
                case 16:
                    bothWord = "sixteen";
                    break;
                case 17:
                    bothWord = "seventeen";
                    break;
                case 18:
                    bothWord = "eighteen";
                    break;
                case 19:
                    bothWord = "nineteen";
                    break;
                default:
                    break;

            }
            if (num <10 && num>0)
            {
                Console.WriteLine(secWord);
            }
            else if (num>=10 && num <20)
            {
                Console.WriteLine(bothWord);
            }
            else  if (num >= 20 && num <=100)
            {
                if (num/10==0 && num!=10 && num!=100)
                {
                    Console.WriteLine(firstWord);
                }
                else if (num==100)
                {
                    Console.WriteLine("one hundred");
                }
                else
                    Console.WriteLine(firstWord + " " +secWord);

            }
            else if (num == 0)
            {
                Console.WriteLine("zero");
            }

            else
            {
                Console.WriteLine("invalid number");
            }

        }
    }
}