def calculate_average():
    how_many_numbers = int(input("How many numbers? "))
    
    if how_many_numbers > 0:
        sum_numbers = 0
        for i in range(0, how_many_numbers):
            number = float(input("Enter a number: "))
            sum_numbers += number

        average = 0
        average = sum_numbers / how_many_numbers

        return average
    else:
        return "Nothing happens."