q1mult3or5

This file is to answer question 1 of Project Euler https://projecteuler.net/
The question is: 

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.