Multiples 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 \( 23 \).

Find the sum of all the multiples of \( 3 \) or \( 5 \) below \( 1000 \).