using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Enter a two digit number");

        int a=int.Parse(Console.ReadLine());

        int i=a/10;

        int j=a%10;

        if(a<19)

        {

            switch(a)

        {   case 1:Console.Write(" one");

            break;

            case 2:Console.Write(" two");

            break;

            case 3:Console.Write(" three");

            break;

            case 4:Console.Write(" four");

            break;

            case 5:Console.Write(" five");

            break;

            case 6:Console.Write(" six");

            break;

            case 7:Console.Write(" seven");

            break;

            case 8:Console.Write(" eight");

            break;

            case 9:Console.Write(" nine");

            break;

            case 10:Console.Write("ten");

            break;

            case 11:Console.Write("eleven");

            break;

            case 12:Console.Write("twelve");

            break;

            case 13:Console.Write("thirteen");

            break;

            case 14:Console.Write("fourteen");

            break;

            case 15:Console.Write("fifteen");

            break;

            case 16:Console.Write("sixteen");

            break;

            case 17:Console.Write("seventeen");

            break;

            case 18:Console.Write("eighteen");

            break;

            case 19:Console.Write("nineteen");

            break;

        }}

        else

        {

        if(i>10)

        {Console.WriteLine("invalid input");}

        else

        {

        switch(i)

        {

        case 0:Console.Write(" ");

        break;

        case 2:Console.Write("twenty");

        break;

        case 3:Console.Write("thirty");

        break;

        case 4:Console.Write("fourty");

        break;

        case 5:Console.Write("fifty");

        break;

        case 6:Console.Write("sixty");

        break;

        case 7:Console.Write("seventy");

        break;

        case 8:Console.Write("eighty");

        break;

        case 9:Console.Write("ninty");

        break;

        }

        switch(j)

        {

            case 1:Console.Write(" one");

            break;

            case 2:Console.Write(" two");

            break;

            case 3:Console.Write(" three");

            break;

            case 4:Console.Write(" four");

            break;

            case 5:Console.Write(" five");

            break;

            case 6:Console.Write(" six");

            break;

            case 7:Console.Write(" seven");

            break;

            case 8:Console.Write(" eight");

            break;

            case 9:Console.Write(" nine");

            break;

            case 10:Console.Write("ten");

            break;

        }}

        }

        }}

​