This is a number guessing Python code ,but it stops after entering the first guessing number. Can you tell me where is the fault?

import random
winning_number = random.randint(1,100)
guess = 1
number = int(input("guess a number between 1 and 100: "))
while not game_over:
  if number == winning_number:
    print(f"you win, and you guessed this number in {guess} times ")
    game_over = True
  else:
    if number < winning_number:
      print("too low")
      guess += 1
      number = int(input("guess again: "))
    else:
      print("too high")
      guess += 1
      number = int(input("guess again: "))

I want to continue the guessing number until it reach the right answer.