def int_check():

    error = "Please enter an integer more than or equal to 13."

    while True:

        try:
            response = int(input("What is the game goal? "))

            if response < 13:
                print(error)

            else:
                return response

        except ValueError:
            print(error)

# main routine starts here
game_goal = int_check()
print(game_goal)