0-100

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

namespace _16.Number0100ToText
{
    class Number0100ToText
    {
        static void Main(string[] args)
        {
            int inputNumber = int.Parse(Console.ReadLine());

            int firstDigit = inputNumber / 10;
            int secondDigit = inputNumber % 10;

            string result = string.Empty;
            if (inputNumber < 0 || inputNumber > 100)
            {
                result = "invalid number";
            }
            else if (inputNumber == 100)
            {
                result = "one hundred";
            }
            else
            {

                switch (firstDigit)
                {
                    case 1:
                        switch (secondDigit)
                        {
                            case 0:
                                result = "ten";
                                break;
                            case 1:
                                result = "eleven";
                                break;
                            case 2:
                                result = "twelve";
                                break;
                            case 3:
                                result = "thirteen";
                                break;
                            case 4:
                                result = "fourteen";
                                break;
                            case 5:
                                result = "fifteen";
                                break;
                            case 6:
                                result = "sixteen";
                                break;
                            case 7:
                                result = "seventeen";
                                break;
                            case 8:
                                result = "eighteen";
                                break;
                            case 9:
                                result = "nineteen";
                                break;
                            default:
                                break;
                        }

                        Console.WriteLine(result);
                        return;
                    case 2:
                        result = "twenty ";
                        break;
                    case 3:
                        result = "thirty ";
                        break;
                    case 4:
                        result = "forty ";
                        break;
                    case 5:
                        result = "fifty ";
                        break;
                    case 6:
                        result = "sixty ";
                        break;
                    case 7:
                        result = "seventy ";
                        break;
                    case 8:
                        result = "eighty ";
                        break;
                    case 9:
                        result = "ninety ";
                        break;

                    default:
                        break;
                }

                switch (secondDigit)
                {
                    case 0:
                        if (firstDigit == 0)
                        {
                            result += "zero";
                        }
                        break;
                    case 1:
                        result += "one";
                        break;
                    case 2:
                        result += "two";
                        break;
                    case 3:
                        result += "three";
                        break;
                    case 4:
                        result += "four";
                        break;
                    case 5:
                        result += "five";
                        break;
                    case 6:
                        result += "six";
                        break;
                    case 7:
                        result += "seven";
                        break;
                    case 8:
                        result += "eight";
                        break;
                    case 9:
                        result += "nine";
                        break;
                    default:
                        break;
                }
            }

            Console.WriteLine(result.TrimEnd());
        }
    }
}