This is a more general solution to the Projecteuler first problem which states : "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." I just replaced 1000 with a parameter provided by the user.