def vowels(s):
    if len(s) == 0:
        return 0
    elif s[0] in 'aeiou':
        return 1 + vowels(s[1:])
    else:
        return vowels(s[1:])
    
def vowels2(s):
    count = 0
    while len(s) > 0:
        if s[0] in 'aeiou':
            count += 1
        s = s[1:]
    return count