link:https://www.codewars.com/kata/514b92a657cdc65150000006
Multiple of 3 or 5
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. Finish the solution so that it returns the sum of all the multiples of 3 or 5 below the number passed in. Note: If the number is a multiple of both 3 and 5, only count it once.