sherlock_and_the_beast.rb

def virus_finder(n)
  rest = n
  total_five = 0
  total_three = 0

  while(rest >= 3 || rest >= 5)
    if(rest % 3 == 0)
      rest -= 3
      total_five += 3
    elsif(rest % 5 == 0)
      rest -= 5
      total_three += 5
    else
      rest -= 3
      total_five += 3
    end
 
    if(rest == 0)
      return "5" * total_five + "3" * total_three
    end
  end

  -1
end