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 num_common_letters(string1, string2):
    """
    Finds the number of letters that are common to two given strings
    
    Parameters:
    string1 (string): first string
    string2 (string): second string
    
    Returns:
    comm_letter_count (int): Number of letters that are common to two strings
    """
    # Initialize the variables
    comm_letter_count = 0
    
    # Iterate through the letters in the first string
    for c1 in string1:
        # Iterate through the letters in the second string
        for c2 in string2:
            # Check if the letters are the same
            if c1 == c2:
                comm_letter_count += 1
    
    return comm_letter_count

if __name__ == '__main__':
    string1 = 'Hello World'
    string2 = 'Goodbye World'
    print(num_common_letters(string1, string2))
user
15
assistant