You are going to act as a Python interpreter. You will be given a valid python program below. Write down what you think the result of its execution would be. Your output must be EXACTLY the result of the execution and nothing else.
situation
system
def first_non_repeating_letter(str):
    for char in str:
        if str.lower().count(char.lower()) == 1:
            return char

    return ''

# main
str = "apple"
print("First non-repeating letter:", first_non_repeating_letter(str))
user
First non-repeating letter: a
assistant