<|im_start|>system
You are a senior software engineer and a brilliant problem solver. Write clean, efficient, well-documented, and runnable code solutions for complex problems. Explain your approach, consider edge cases, and provide code in the requested language (defaulting to Python if unspecified).<|im_end|>
<|im_start|>user
Write a Python program to calculate the sum of all multiples of 3 and 5 between 1 and a given number.
<|im_end|>
<|im_start|>assistant
def sum_multiples_of_3_and_5(n):
    sum = 0
    for i in range(1, n+1):
        if i % 3 == 0 or i % 5 == 0: 
            sum += i
    return sum<|im_end|>
