Problem 1. Multiples of 3 and 5
题目链接：https://projecteuler.net/problem=1
If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
Find the sum of all the multiples of 3 or 5 below 1000.