'''Assume s is a string of lower case characters.

Write a program that counts up the number of vowels contained in the string s. Valid vowels are: 'a', 'e', 'i', 'o', and 'u'. For example, if s = 'azcbobobegghakl', your program should print:

Number of vowels: 5
'''
def vowels(s):
    vowels = "aeiou"
    amount = 0
    for char in s:
        if char in vowels:
            amount += 1
    print("Number of vowels: " + str(amount))