help

def register():
    global admin
    create_user = input("Create your username: ")
    create_pass = input("Create your password: ")
    f = open("users.txt" , "a")
    f.write (create_user + ' : ' + create_pass, admin + "\n")


    f.close===========
error message
=============================

Exception has occurred: TypeError
unsupported operand type(s) for +: 'int' and 'str'
  File "D:\Desktop\python\login.py", line 29, in register
    f.write (create_user + ' : ' + create_pass, admin + "\n")
  File "D:\Desktop\python\login.py", line 18, in start
    register()
  File "D:\Desktop\python\login.py", line 94, in <module>
    start()