'Casting irresponsive

Tried to do casting on this little project I am working on can anyone tell me what I have done wrong?

Calculation_to_units = 24 
name_of_unit = "hours"

def days_to_units(num_of_days): 
    if num_of_days > 0: 
        return f"{num_of_days} days are {num_of_days * Calculation_to_units} {name_of_unit}" 
    else: 
        return "You enter a negative value, so no conversion can happen"

user_input = input("Hey user, enter the number of days and i will convert it into hours\n") 
user_input_number = int(user_input)

calculated_value = days_to_units(user_input_number)


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