How to make one Inputfield Logon

Hi Everyone, (sorry for a long post, couldn't find the answer) I have figure out how to create a Logon system which you can register or login in to the game. It does not use online servers and it save the file offline and check the password. I have a problem the Logon system use 4 Input field but I can't figure out how to only use one input field for registration, to create a password and username and have another field for Login username and password , Hope you get what I mean, I provide some image such as this

Here is also my Scripts

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using System;
 
 
 public class Reg : MonoBehaviour {
     public GameObject username;
     public GameObject password;
 
     private string UserName;
     private string PassWord;
     private string Container;
 
     public void Registration(){
         bool UN = false;
         bool PWD = false;
             
         if (UserName != "") { //not UserName not equal to space than perform this task
             if (!System.IO.File.Exists (@"C:/" + username + ".txt")) {//if folder doesnt exist change UN to true
                 UN = true;
             } else { //if file does exist print this
                 print ("Username is taken");
             }
         } else {//if field is empty print this
             print ("Please create a Username");
         }
 
         if (PassWord != "") {
             if (PassWord.Length > 4) {
                 PWD = true;
             } else {
                 print ("Not enough character it need to be 6 or more");
             } 
         } else {
             print ("Please create a Password");
         }
 
         if (UN == true && PWD == true) {
             bool Clear = true;
             int i = 1;
             foreach (char c in PassWord) {
                 if (Clear) {
                     PassWord = "";
                     Clear = false;
                 }
                 i++;
                 char Encrypted = (char)(c * i);
                 PassWord += Encrypted.ToString ();
             }
             Container = (UserName + Environment.NewLine + PassWord);
             System.IO.File.WriteAllText (@"C:/Programs/" + UserName + ".txt", Container);
             username.GetComponent<InputField> ().text = "";
             password.GetComponent<InputField> ().text = "";
             print ("Registration Complete");
         }
     }
 
     void Update () {
 
         if (Input.GetKeyDown(KeyCode.Return)){
             if (PassWord != ""/*&&Email != ""&&Password != ""/*&&ConfPassword != ""*/){
                 Registration();
             }
         }
         UserName = username.GetComponent<InputField>().text;
         //Email = email.GetComponent<InputField>().text;
         PassWord = password.GetComponent<InputField>().text;
         //ConfPassword = confPassword.GetComponent<InputField>().text;
     }
 
 
 
 
 }

//Logon Script

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 using System;
 using System.Text.RegularExpressions;
 
 public class Logon : MonoBehaviour {
 
     public GameObject username;
     public GameObject password;
     private string UserName;
     private string PassWord;
     private String[] Lines;
     private string DecryptedPass;
 
     public void LoginButton(){
         bool UN = false;
         bool PWD = false;
         if (UserName != ""){
             if(System.IO.File.Exists(@"C:/Programs/"+UserName+".txt")){
                 UN = true;
                 Lines = System.IO.File.ReadAllLines(@"C:/Programs/"+UserName+".txt");
             } else {
                 Debug.LogWarning("UserName Incorrect");
             }
         } else {
             Debug.LogWarning("Please Reg");
         }
         if (PassWord != ""){
             if (System.IO.File.Exists(@"C:/Programs/"+UserName+".txt")){
                 int i = 1;
                 foreach(char c in Lines[1]){
                     i++;
                     char Decrypted = (char)(c / i);
                     DecryptedPass += Decrypted.ToString();
                 }
                 if (PassWord == DecryptedPass){
                     PWD = true;
                 }
             } else {
                 Debug.LogWarning("Password Is invalid");
             }
         } else {
             Debug.LogWarning("Password Field Empty");
         }
         if (UN == true&&PWD == true){
             username.GetComponent<InputField>().text = "";
             password.GetComponent<InputField>().text = "";    
             print ("Login Sucessful");
             Application.LoadLevel("Start Menu");
         }
     }
     // Update is called once per frame
     void Update () {
         if (Input.GetKeyDown(KeyCode.Tab)){
             if (username.GetComponent<InputField>().isFocused){
                 password.GetComponent<InputField>().Select();
             }
         }
         if (Input.GetKeyDown(KeyCode.Return)){
             if (PassWord != ""&&PassWord != ""){
                 LoginButton();
             }
         }
         UserName = username.GetComponent<InputField>().text;
         PassWord = password.GetComponent<InputField>().text;    
     }
 }