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.

My solution in Ruby:

sum = 0
for i in 1..999
  sum += i if i % 3 == 0 or i % 5 == 0
end

puts sum