number to words in lithuanian, C#

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//Title of this code
//Rextester.Program.Main is the entry point for your code. Don't change it.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            //Your code goes here
            Console.WriteLine(GetNumberInWords("54"));
        }
        
        public static string GetNumberInWords(string n)
        {
            if (string.IsNullOrEmpty(n))
                return "";

int number = Convert.ToInt32(n);
            if(number == 0)
                return "nulis";
            
            int type = 0;
            int remainder = number;
            string res = "";
            if (number % 100 > 9 && number % 100 < 20)
            {
                res = GetPartInWords(number % 100, 1);
                type = 2;
                remainder = number / 100;
            }
            while (remainder != 0)
            { 
                type++;
                int factor = 10;
                if(type >= 4)
                    factor = 1000;
                res = GetPartInWords(remainder % factor, type).Trim() + " " + res.Trim();
                remainder = remainder / factor;
            }

return res;
        }
        static string GetPartInWords(int number, int type)
        {
            if (type == 1) //0-19
            {
                switch (number)
                { 
                    case 1:
                        return "vienas";
                    case 2:
                        return "du";
                    case 3:
                        return "trys";
                    case 4:
                        return "keturi";
                    case 5:
                        return "penki";
                    case 6:
                        return "šeši";
                    case 7:
                        return "septyni";
                    case 8:
                        return "aštuoni";
                    case 9:
                        return "devyni";
                    case 10:
                        return "dešimt";
                    case 11:
                        return "vienuolika";
                    case 12:
                        return "dvylika";
                    case 13:
                        return "trylika";
                    case 14:
                        return "keturiolika";
                    case 15:
                        return "penkiolika";
                    case 16:
                        return "šešiolika";
                    case 17:
                        return "septyniolika";
                    case 18:
                        return "aštuoniolika";
                    case 19:
                        return "devyniolika";
                }
            }
            if (type == 2)  //20,30,40,50,60,70,80,90
            {
                switch (number)
                { 
                    case 2:
                        return "dvidešimt";
                    case 3:
                        return "trisdešimt";
                    case 4:
                        return "keturiasdešimt";
                    case 5:
                        return "penkiasdešimt";
                    case 6:
                        return "šešiasdešimt";
                    case 7:
                        return "septyniasdešimt";
                    case 8:
                        return "aštuoniasdešimt";
                    case 9:
                        return "devyniasdešimt";
                }
            }
            if (type == 3) //100, 200, 300, 400, 500, 600, 700, 800, 900
            {
                switch (number)
                { 
                    case 1:
                        return "vienas šimtas";
                    case 2:
                        return "du šimtai";
                    case 3:
                        return "trys šimtai";
                    case 4:
                        return "keturi šimtai";
                    case 5:
                        return "penki šimtai";
                    case 6:
                        return "šeši šimtai";
                    case 7:
                        return "septyni šimtai";
                    case 8:
                        return "aštuoni šimtai";
                    case 9:
                        return "devyni šimtai";
                }
            }
            if (type == 4)  //tūkstančiai
            {
                if(number % 1000 != 0)
                {
                    List<string> vns_vardininkas = new List<string>()
                    {
                        "01", "21", "31", "41", "51", "61", "71", "81", "91" 
                    };
                    List<string> kilmininkas = new List<string>()
                    {
                        "00", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "30", "40", "50", "60", "70", "80", "90"
                    };
                    
                    var last_two = (number % 100).ToString().PadLeft(2, '0');
                    var word = "tūkstančiai";
                    if(vns_vardininkas.Contains(last_two))
                        word = "tūkstantis";
                    if(kilmininkas.Contains(last_two))
                        word = "tūkstančių";
                    
                    return GetNumberInWords(number.ToString()).Trim()+" "+word.Trim();
                }
                else
                {
                    return "";
                }
            }
            if (type == 5) //milijonai
            {
                if(number % 1000 != 0)
                {
                    List<string> vns_vardininkas = new List<string>()
                    {
                        "01", "21", "31", "41", "51", "61", "71", "81", "91" 
                    };
                    List<string> kilmininkas = new List<string>()
                    {
                        "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "30", "40", "50", "60", "70", "80", "90"
                    };
                    
                    var last_two = (number % 100).ToString().PadLeft(2, '0');
                    var word = "milijonai";
                    if(vns_vardininkas.Contains(last_two))
                        word = "milijonas";
                    if(kilmininkas.Contains(last_two))
                        word = "milijonų";
                    
                    return GetNumberInWords(number.ToString()).Trim()+" "+word.Trim();
                }
                else
                {
                    return "";
                }                
            }
            if (type == 6) //milijardai
            {
                if(number % 1000 != 0)
                {
                    List<string> vns_vardininkas = new List<string>()
                    {
                        "01", "21", "31", "41", "51", "61", "71", "81", "91" 
                    };
                    List<string> kilmininkas = new List<string>()
                    {
                        "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "30", "40", "50", "60", "70", "80", "90"
                    };
                    
                    var last_two = (number % 100).ToString().PadLeft(2, '0');
                    var word = "milijardai";
                    if(vns_vardininkas.Contains(last_two))
                        word = "milijardas";
                    if(kilmininkas.Contains(last_two))
                        word = "milijardų";
                    
                    return GetNumberInWords(number.ToString()).Trim()+" "+word.Trim();
                }
                else
                {
                    return "";
                }
            }
            return "";
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0.34 sec, absolute running time: 0.19 sec, cpu time: 0.14 sec, average memory usage: 18 Mb, average nr of threads: 4