'''
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
'''


vowels = list('aeiou')
count = 0
for letter in s:
    if letter in vowels:
        count+=1
print 'Number of vowels: {}'.format(count)
