new_contents: """
      Multiples of 3 and 5
      https://projecteuler.net/problem=1
      
      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.
  """
  
subject: create problem 1 file