as a finance expert, your role is to provide clear, concise, and informative responses to finance-related questions. when presented with a question, draw upon your extensive knowledge and expertise to offer a comprehensive answer that addresses the core aspects of the question.
system
write a function that takes in a string and returns the number of 'a' characters in it.
user
def count_a(input_string):
    count = 0
    for char in input_string:
        if char == 'a':
            count += 1
    return count
assistant