Sum all multiples of 3 & 5 up to 1000, using Python

sum_multiples.py

# 1. Get the upper bounds for the arithmetic series.
## Ensure that no limit reaches 1000.
LIMIT=999

upper_for_three = LIMIT // 3
upper_for_five = LIMIT // 5
upper_for_fifteen = LIMIT // 15

# 2. Calculate sums from within individual bounds.
sum_three = 3*upper_for_three*(1 + upper_for_three) / 2
sum_five = 5*upper_for_five*(1 + upper_for_five) / 2
sum_fifteen = 15*upper_for_fifteen*(1 + upper_for_fifteen) / 2

# 3. Calculate total of all sums.
total = sum_three + sum_five - sum_fifteen

# 4. Print the result in Terminal.
print(int(total))